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OF  CALIFORNIA 

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LOGIN  BROi 

MEDICAL    BOO 


Dynamic  Skiametry 

in 

Theory  and  Practice 

Embracing   Its   Association   with   Static  Skiametry   and 

with  Those  Optometric  Methods  Wherein  the 

Correlation  of  Accommodation  and 

Convergence   Must   Be 

Considered 

BY 

ANDREW  JAY  CROSS,  D.O.S. 

Author  of  "A    System   of  Ocular    Skiametry."      Lecturer   on   Theoretic   and    Practical 

Optometry,  Columbia  University.      President  American  Optical  Association  1900-01, 

and  Honorary  Life  Member  of  Its  Scientific  Section.    President  Optical  Society 

State  of  New  York  1897-98-99-1900.    Dean  of  The  New  York  Institute 

of  Optometry  1907  08-09.      Honorary  Member  Rochester,  N.  Y., 

and    Syracuse,    N.     Y.,    Optometric    Societies,    etc.,    etc. 


IVith  Seventy-One  Illustrations 

(Sixty-one  of  which  are  Original  Drawings) 


PUBLISHED   BY 

A.  JAY  CROSS  OPTICAL  COMPANY 

20  East  Twenty-third  Street 
New  York 


COPYRIGHT,    191 1,   BY    ANDREW    JAY   CROSS 


Press  of  S.  L.  Parsons  &  Co. 
45    Rose    Stueet,    New    York 


O\on(r0 
VJVJ 

nil 


To 

My  Colleague, 

CHARLES  F.  PRENTICE,  M  E., 

One  of  the  First  to  Recognize  the  Scientific  Value  of  Dynamic 
Skiametry,  and  With  Whom  I  Have  Been  Associated  in  Opto- 
METRic  Organization  and  Education  Work  Since  1895,  This  Little 
Volume  is  Affectionately  Dedicated. 


PREFACE 

The  progress  made  in  optometry  during  the  past  decade  has 
perhaps  been  influenced  by  no  one  division  more  than  it  has 
by  that  of  Dynamic  Skiametry,  for  the  revolutionary  character 
of  this  new  objective  method  has  of  necessity  developed  many 
minor  factors  which  were  unknown  when  the  former  book,  "A 
System  of  Ocular  Skiametry,"  was  issued. 

For  this  reason  it  is  now  deemed  wise  to  present  new  expla- 
nations of  the  theory  and  practice  of  dynamic  shadow  testing 
and,  at  the  same  time,  retain  all  of  the  old  that  has  been  found 
good. 

Static  skiametry,  or  that  method  known  by  the  blanket  term 
"retinoscopy,"  has  been  explained  so  often  by  other  writers  that 
it  is  thought  quite  unnecessary  to  add  to  the  length  of  this  little 
volume  further  than  by  a  brief  description  of  the  cardinal 
points  involved,  hence  it  will  be  taken  for  granted  that  the 
reader  is  more  or  less  familiar  with  the  optical  principles  under- 
lying Bowman's  great  discovery,  and  with  the  added  improve- 
ments made  by  Cuignet  and  athers  prior  to  1902,  when  the 
dynamic  method  was  originated  and  made  public  by  the  author. 

New  York, 
October,  1911. 


CONTENTS 

CHAPTER    I Pages  15  to  26 

Ocular  Skiametry  as  a  System,  Its  Value  in  Optometry  and  the 
Optical  Knowledge  Necessary  to  Master  It,  Including  Difficulties 
to  be  Overcome. 

CHAPTER    II Pages  27  to  46 

Proper  and  Improper  Examination  Rooms,  Size  Intensity  and 
Control  of  Illumination,  the  Plane  Skiascope,  How  to  Handle 
It,  and  Some  Novel  Inventions. 

CHAPTER    III Pages  47  to  59 

Schematic  Eye  Practice  and  Its  Importance  to  Students,  Model 
Eyes  and  the  Exercise  of  Care  in  Their  Adjustment.  Reduction 
and  Transposition  of  Lens  Values,  and  the  Necessity  for  the 
Complete  Mastery  of  This  Work  in  Successful  Skiametry. 

CHAPTER    IV Pages  60  to  79 

Why  Ocular  Pupils  Appear  Red  When  Viewed  Through  a  Skia- 
scope, With  a  Brief  Description  of  the  Cardinal  Points  Involved 
in  Static  Skiametry  as  Practiced  With  the  Plane  Mirror,  Includ- 
ing Some  Theories  Regarding  Fundus  Reflex. 

CHAPTER    V Pages  80  to  99 

Theory  of  Dynamic  Skiametry,  and  the  Importance  of  Reliable 
Fixation  in  Co-ordinate  and  Independent  Observation,  With  a 
Reference  to  Three  Essential  Myopias,  and  an  Explanation  of 
"Ray  Values". 

CHAPTER    VI Pages  100  to  114 

Orthophoria  and  Heterophoric  Conditions,  and  the  Influence  of 
Habit  Upon  Accommodation  and  Convergence,  With  Special 
Consideration  of  Spasms  and  the  Use  of  Prisms. 

CHAPTER    VII Pages  115  to  123 

Practice  of  Dynamic  Skiametry,  Its  Use  in  Measuring  Regular  and 
Irregular  Astigmia,  and  Its  Special  Value  in  the  Objective  Esti- 
mation of  Presbyopia  and  Sub-Normal  Accommodation,  To- 
gether With  Its  Relationship  to  Other  Methods  and  Tests. 


CONTENTS— Continued 

CHAPTER    VIII Pages  124  to  137 

Illustrative  Cases,  Showing  the  Comparative  Value  of  Static  and 
Dynamic  Skiametry  in  Patients  of  Different  Ages,  Occupation 
and  General  Physical  Condition. 

CHAPTER    IX Pages  138  to  152 

Multiple  Methods  in  Optometry  and  Their  Value  in  Corroborative 
Measurements,  the  Systematic  Keeping  of  Records  and  the  Im- 
portance of  "Case  History",  Including  Resourcefulness  and 
Mechanical  Mydriasis. 

CHAPTER  X Pages  153  to  172 

Value  of  Instruments  in  Practising  Optometry.  Mobile  and  Unit 
Lens  Systems,  Various  Instruments  Used  in  Skiametry,  With 
Description  of  Their  Mechanical  Construction. 

CHAPTER  XI Pages  173  to  196 

Questions  and  Answers  Pertaining  to  Static  and  Dynamic  Ski- 
ametry and  Correlated  Subjects.  With  Pertinent  Remarks  Em- 
phasizing the  Salient  Points  Involved. 

CHAPTER  XII Pages  197  to  218 

Opinions  of  Others  Regarding  the  Value  of  Skiametry  in  General 
and  the  Dynamic  Method  in  Particular,  With  Comments  on 
Objective  Versus  Subjective  Optometry,  and  the  Relationship  of 
Accommodation  and  Convergence,  Including  Quotations  on 
Mental  Perception,  and  an  Epilogue. 


ILLUSTRATIONS 

Fig.  Page 

1  Parallel    rays    of    light    converged 20 

2  Divergent  rays  of  light  paralleled 20 

3  Acetylene  gas  lamp  with  metal  chimney 30 

4  Asbestos  lined  metal  chimney 31 

5  Asbestos  lined  glass  chimney 32 

6  Asbestos-paper  chimney-cover  with   iris  diaphragm  opening..  33 

7  Spiral  filament  in  electric   lamp 34 

8  Author's  asbestos  covered  electric  lamp 36 

9  DeZeng   electric    retinoscope 37 

10  The  "Hardy"  wall  bracket  for  gas  or  electric  lamp 38 

11  A  simple  skiascope 40 

12  Author's  double  bracket  skiascope 41 

13  Skiametric    fixation   card 42 

14  Skiametric  fixation  card 42 

15  Manner  of  holding  author's  skiascope 43 

16  Reisner's  retinoscope   45 

17  Klein's  retinoscope   46 

18  DeZeng-Standard  schematic  eye 48 

19  Queen's  pasteboard  schematic  eye 49 

20  Two  cylindric  lenses  of  unequal  focus  and  axis 52 

21  A  crossed  cylinder-lens  of  unequal  meridional  focus 53 

22  Three  cylindric  lenses  of  equal  focus,  one  at  axis  90,  and  two 

at  axis  180 53 

23  One    crossed    cylinder   of    equal    meridional    focus    and    one 

simple  cylinder  at  axis  180 54 

24  Crossed  cylindric  lens  of  plus  and  minus  curvatures 57 

25  Three  cylindric  lenses,  two  plus  and  one  minus 58 

26  Illumination  of  second  card  through  hole  in  first  one 61 

27  Return  rays  from  second  card  entering  eye  through  tube  in 

candle  61 

28  Substituting  a  skiascope  for  candle  tube 62 

29  Illuminating  the  ocular  fundus 64 

30  The  illuminated  area  on  the  fundus 65 


ILLUSTRATIONS— Continued. 
Fig.  Page 

31  Rays  returning  from  edge  of  illuminated  area  on  the  fundus. . .  65 

32  Returning  rays  influenced  by  a  convex  lens 66 

33  Why  the  shadow  moves  "with"  the  mirror 67 

34  Why  the  shadow  moves  "against"  the  mirror 68 

35  Pupillary  appearance  of  a  so-called  "shadow" 69 

36  Why  the   retinal  illumination  is   larger  in  ametropia  than  in 

emmetropia    74 

37  Why  shadows  move  slower  in  ametropia  than  in  emmetropia..     7$ 

38  Why  a  shadow  is  duller  in  myopia  than  in  a  like  degree  of 

hypermetropia    76 

39  Relative  size  of  retinal  illumination  in  high  and  low  degrees 

of  myopia 77 

40  The  optical  principles  of  penumbra 77 

41  The  optical  principles  of  penumbra  doubled 78 

42  Interference  of  penumbra  in  shadow  testing 79 

43  True  myopia    ( Static  Method)    84 

44  Artificial  myopia   ( Static  Method) 85 

45  Accommodative   myopia    (Dynamic  Method) 86 

46  How  the  accommodation  can  absorb  a  ciliary  spasm 88 

47  Multiple  fixation  and  observation  points 91 

48  Author's    fixation    stand 92 

49  Fixation  stand  target  card 93 

50  Reverse  side  of  fixation  card 93 

51  Position  for  initial   examination 94 

52  Balancing  the  accommodation  and  convergence  in  emmetropia.  104 

53  Equal   innervation   necessary  to  balance  accommodation   and 

convergence    in    emmetropia 105 

54  Imbalance   of  accommodation   and   convergence   in   hyperme- 

tropia       106 

55  Unequal  innervation  required  to  balance  accommodation  and 

convergence   in  hypermetropia 106 

56  Imbalance  of  accommodation  and  convergence  in  myopia 107 

57  Unequal  innervation  required  to  balance  accommodation  and 
convergence   in  myopia 107 


ILLUSTRATIONS— Continued. 

Fig.  Page 

58  Author's  record  blank 145 

59  Regular  size  pupil 151 

60  Area  of  mag^nified  pupil 151 

61  Refraction  by  lenses  placed  close  together 154 

62  Refraction  by  lenses  separated 155 

63  King's  binocular  hand  trial  set 156 

64  Skiametric  lens  rack  of  Wiirdemann 158 

65  Lens  disc  used  by  Grain  and  others 159 

66  Standart's  "Umbrameter"  160 

67  The  Meriden  "Oculometroscope"   162 

68  The  "Geneva"  retinoscope  164 

69  DeZeng's  Optometer,  Phorometer  and  Skiameter 167 

70  Constructive  principle  of  the  author's  skiameter 170 

71  Author's  skiameter  without  base 171 


Dynamic  Skiametry 

in 
Theory  and  Practice 


CHAPTER  I. 

Ocular  Skiametry  as  a  System. — Its  Value  in  Optometry 
AND  THE  Optical  Knowledge  Necessary  to  Master  It, 
Including  Difficulties  to  be  Overcome. 

SKIAMETRY  AS  A  SYSTEM.  Formerly  there  was 
only  one  method  employed  in  measuring  eyes  by  the  so-called 
shadow  test,  and  this  one  method  was  made  to  do  service  for 
the  six-year-old  child  and  the  sixty-year-old  adult. 

This  one  method  was  also  employed  for  measuring  the 
myope  of  high  degree  and  the  hypermctrope  of  low.  Long 
standing  habits  of  suppression  of  accoinmodation  or  conver- 
gence, due  to  impaired  co-ordination,  were  entirely 'ignored  and 
presbyopia  was  never  a  factor  to  be  considered.  Indeed,  all 
eyes,  like  all  Chinamen,  were  said  to  "look  alike." 

It  is  not  many  years  since  eminent  authorities  claimed 
that  the  recognition  and  correction,  with  lenses,  of  hyperopic 
errors  of  less  than  one  diopter  was  equivalent  to  taking  an  un- 
fair advantage  of  a  patient,  and  therefore  savored  of  charletan- 
ism.  What  is  now  known  as  eye  strain  was  classified  as  latent 
hypermetropia  and  of  trifling  importance  unless  of  high  degree. 

But  the  foreword  in  optometry,  particularly  during  the  past 
few  years,  has  been  to  pay  more  attention  to  minor  details  for, 
as  in  other  walks,  both  service  and  comfort  are  often  secured  by 
giving  heed  to  the  little  things.  This  care  and  attention  has 
developed  the  fact  that  greater  accuracy  in  shadow  testing  can 
only  be  obtained  by  applying  methods  which  take  into  consid- 
eration the  patient's  age,  and  other  previously  overlooked  factors 
requiring  varying  procedure  in  varying  cases. 

The  word  "system"  is  defined  as  "a  series  of  methods,"  so 


1 6  SKIAMETRY  AS  A  SYSTEM 

it  is  easy  to  understand  why  ocular  skiametry  or,  literally,  eye- 
shadow-measuring, came  to  be  known  as  a  system  of  ocular 
skiametry. 

VALUE  OF  SKIAMETRY.  In  the  general  practice  of 
his  profession  the  most  difficult  problem  that  confronts  the 
optometrist  is  the  fitting  of  his  patient's  preconceived  notions 
as  to  the  kind  of  glasses  needed,  and  the  manner  in  which  they 
are  to  be  worn,  so  in  attempting  to  make  plain  the  true  value 
of  static  and  dynamic  skiametry  the  problem  which  confronts  the 
writer  is  the  overcoming  of  the  previously  formed  opinion  that 
most  readers  have,  for  many  inquirers  into  the  merits  of 
shadow  testing  seem  to  be  possessed  with  the  belief  that  every 
case  which  presents  itself  is  capable  of  being  both  easily  and 
accurately  refracted  by  means  of  Bowman's  great  discovery. 
This  expectation  being  as  inconsistent  with  the  real  facts  as  it 
would  be  to  expect  like  results  from  trial  case  tests  or  by  any 
other  one  optometric  method. 

The  truth  can  perhaps  be  fairly  expressed  by  saying  that 
shadow  testing  bears  to  trial  case  testing  much  the  same  rela- 
tion that  the  addition  of  a  column  of  figures  from  the  top  bears 
to  its  addition  from  the  bottom. 

Skiametry  will  uncover  at  a  single  sitting  optical  conditions 
which  it  would  be  quite  impossible  for  ordinary  trial  case  tests 
to  do.  On  the  other  hand,  the  latter  will  show  visual  conditions 
of  which  the  former  can  tell  nothing.  Viewed  again  from  a 
similar  position  we  find  that  the  two  general  methods  for  esti- 
mating ocular  errors  of  refraction,  known  by  the  terms  objective 
and  subjective,  are  like  seeing  for  one's  self  and  taking  the 
testimony  of  others.  Usually  either  method  is  fairly 
reliable  in  ordinary  cases,  but  in  extraordinary  ones — the  kind 
that  make  and  break  reputations — the  evidence  can  be  none 
too  corroborative. 

So  we  find  skiametric  and  trial  case  testing  to  be  inter-de- 
pendent, both  systems  having  their  weak  and  strong  points,  and 


VALUE    OF    SKIAMETRY  1 7 

one  aiding  in  the  judgment  requisite  for  the  successful  appUca- 
tion  of  the  other,  skiametry  coming  first  because  it  is  the  great 
refractive  pilot,  or  pathfinder,  and  because,  too,  there  are  many 
conditions,  other  than  errors  of  refraction,  that  are  shown  up 
by  its  use  and  which,  if  it  were  not  for  this  early  use,  might 
needlessly  prolong  an  otherwise  short  examination. 

It  is  hoped,  therefore,  that  this  point  is  made  clear  regard- 
ing the  value  of  shadow  testing.  It  is  deemed  of  no  more  nor 
less  value  than  the  trial  case  test,  and  that  neither  one  is 
infallible,  and  that  both  are  absolutely  essential  in  all  prime 
cases,  whether  the  results  obtained  by  either  coincide  with  those 
of  the  other  or  not,  for  this  very  lack  of  coincidence  is  often  the 
key  which  enables  a  trained  judgment  to  solve  a  refractive 
riddle. 

By  basing  their  judgment  upon  the  principle  that  the  proof 
of  the  pudding  lies  in  interviewing  the  one  who  has  chewed  the 
string,  some  credulous  inquirers  have  been  led  to  estimate  the 
merits  of  shadow  testing  by  taking  the  testimony  of  those  who 
have  falsely  pretended  to  possess  a  thorough  knowledge  of  it, 
and  this  unreliable  information  has  led  them  to  believe  that  if 
skiametry  is  faulty  in  some  hands  it  must  be  faulty  in  all. 
Whereas  the  reverse  reasoning  would  in  all  probability  be  pro- 
ductive of  better  results,  for  that  which  one  can  achieve  by 
study  and  practice  it  is  quite  possible  for  others  to  achieve  by 
equal  application  and  effort,  and  sometimes  by  even  less  where 
assistance  is  given  by  skilled  instructors. 

For  nearly  four  decades  the  ablest  optometric  researchers 
have  striven  their  utmost  to  find  a  better  objective  means  than 
skiametry  for  determining  the  optical  condition  of  eyes,  but  so  far 
without  avail.  And  judging  from  the  present  advanced  knowl- 
edge regarding  optics  and  optometry  it  is  pretty  safe  to  say  that 
the  shadow  test  is  here  to  stay,  for  a  long  time  at  least,  and  that 
those  whose  duty  it  is  to  adapt  glasses  to  the  eyes  of  others  will 
find  their  work  more  reliable  and  much  easier  if  they  will  take 


l8  OPTICAL    KNOWLEDGE    NECESSARY 

the  time  to  thoroughly  master  this  valuable  means  for  ascertain- 
ing ocular  refractive  conditions  in  a  manner  independent  of  the 
patient's  intelligence. 

Now  this  phrase,  "independent  of  the  patient's  intelligence," 
may  prove  somewhat  misleading,  since  even  those  who  are 
experienced  in  skiametric  work  find  many  cases  in  which  the 
results  obtained  are  very  unsatisfactory  indeed.  Yet,  when  an 
examiner  measures  a  case  by  skiametry  and  notes  an  error  of 
refraction  which  later  on  is  confirmed  by  the  trial  case  test,  he 
feels  that  he  has  received  advance  information  of  a  truly  "inde- 
pendent" character,  and  upon  which  he  can  rely  with  greater 
confidence  than  if  this  information  had  been  denied  him.  On 
the  other  hand,  if  the  trial  case  test  does  not  confirm  the  mirror 
findings,  then  the  mirror  is  employed  again  to  confirm  the  trial- 
ca've  findings.  The  subjective  is  used  to  check  the  objective,  and 
then  the  objective  again  to  corroborate  the  subjective. 

OPTICAL  KNOWLEDGE  NECESSARY.  Expressed  in 
a  broad  way,  the  optical  knowledge  necessary  to  achieve  skia- 
metric success  is  all  the  optical  knowledge  a  student  can  obtain. 
But  keeping  in  mind  the  practical  side  of  the  work  there  will 
be  found  a  few  essentials  which  are  clearly  indicated  before 
intelligent  progress  can  be  reasonably  expected. 

The  general  optical  principles  of  the  shadow  test  in  its 
simplest  form  are  not  very  complicated.  Taken,  however,  in 
connection  with  its  optometric  associates  skiametry  represents, 
as  a  whole,  a  rather  high  order  of  knowledge  regarding  both 
physical  and  physiologic  optics.  It  also  requires  in  its  applica- 
tion a  certain  amount  of  skill  or  dexterity  in  the  manipulation  of 
indispensable  mechanical  devices,  such  as  the  skiascope  and  ski- 
ameter, no  matter  whether  the  latter  be  a  simple  trial  frame  with 
test  lenses,  or  a  more  elaborate  and  useful  apparatus. 

There  are  tyvo  leading  accomplishments  in  shadow  testing 
in  which  an  examiner  must  be  proficient  before  he  can  achieve 


OPTICAL    KNOWLEDGE    NECESSARY  I9 

success.  The  first  of  these  is  the  control  of  the  reflected  light 
and  the  determination  of  the  direction  of  the  shadow's  motion, 
under  both  favorable  and  unfavorable  conditions.  The  second 
lies  in  being  able  to  add  and  subtract  known  refractive  lens 
quantities  and  to  tell  with  precision  what  their  ray-bending 
value  is  at  all  distances  from  an  eye  under  examination.  To 
express  it  tersely  then,  an  examiner  must  be  able  to  detect  any 
action  of  the  shadow  and  to  know  exactly  what  the  optical  value 
of  this  action  is  when  influenced  by  either  lenses  or  fixation. 

The  first  of  the  above  requirements  can  be  gained  by  daily 
practice,  but  the  second  requires  considerable  study  and  applica- 
tion, as  it  involves  a  knowledge  of  angles  of  light,  or  ray  values, 
as  well  as  of  refraction,  or  lens  values. 

When  a  patient's  eye  is  considered  as  an  object,  instead  of 
as  a  subject,  then  its  refractive  condition  must  be  determined  by 
noting  the  behavior  of  the  light  reflected  from  the  retina  as  it 
leaves  the  eye,  and  methods  of  procedure  known  as  objective 
must  therefore  be  applied. 

Many  students  of  optics  who  have  confined  their  efforts  to  a 
mastery  of  subjective  optometry  alone  often  find  themselves 
quite  at  sea  when  they  undertake  objective  methods.  And  the 
reason  for  this  usually  lies  in  the  fact  that  they  have  given 
attention  to  the  subject  of  light  as  it  travels  in  but  one  direction, 
namely,  as  it  enters  an  eye. 

One  of  the  foundation  principles  taught  in  optical  text-books 
is  that  light  returns  over  the  same  course  which  it  has  traveled, 
hence  if  parallel  rays  of  light  are  made  to  pass  through  a  convex 
lens  they  will  come  to  a  focus  at  the  so-called  "strength"  of  the 
lens.  Invert  this  order,  by  placing  a  lighted  candle  at  the  focus 
of  the  lens,  and  the  rays  of  light  will  diverge  until  they  pass 
through  the  lens,  after  which  they  will  be  parallel.  See  Figs. 
I  and  2. 

In  shadow  testing  the  retina  of  an  eye  is  the  apparent  source 
of  light,  although  in  reality  the  retina  is  only  a  poor  quality  of 


20 


OPTICAL    KNOWLEDGE    NECESSARY 


mirror  which  reflects  the  Hght  thrown  into  the  eye  by  the  skia- 
scope. This  illumination,  or  reflection,  behaves  like  a  piece 
of  red  flannel,  or  any  other  visible  object  which  acts  as  a  high 
or  low  grade  mirror  according  to  its  ability  to  reflect  light. 
Glass  with  amalgam  backing,  and  polished  metals  being  of  the 
highest  order,  while  lampblack  and  black  velvet  are  of  the 
lowest. 

Fig.  I. 


Focu3 


PARALLEL   RAYS   OF    LIGHT    CONVERGED. 


Fig.  2. 


DIVERGENT    R.\YS    OF    LIGHT    PARALLELED. 


The  correlation  of  accommodation  and  convergence  is  an- 
other subject  which  students  of  ocular  skiametry  must  under- 
stand in  order  to  do  their  work  intelligently.  Thus  it  will  be 
seen  that  skiametric  proficiency  involves  a  pretty  thorough 
grounding  in  something  more  than  rudimentary  optics.  With 
the  elimination  of  the  use  of  the  concave  mirror,  however,  and 


DIFFICULTIES    TO    OVERCOME  21 

by  the  aid  of  modern  apparatus  it  is  now  possible  to  dispense 
with  many  details  which  formerly  resulted  in  the  confusion  of 
beginners.  Still,  notwithstanding  this,  a  student  will  find  much 
that  will  call  forth  his  best  efforts  before  he  can  feel  assured  of 
the  reliability  of  his  findings. 

It  is  one  thing  to  master  ocular  skiametry  under  regular 
conditions  and  quite  another  to  rightly  differentiate  the  irregu- 
lar and  apply  that  judgment  which  secures  success.  But,  as 
in  other  studies,  the  deeper  the  student  delves  the  more  he  finds 
to  learn,  and  the  easier  do  the  foundation  principles  become. 
The  wise  searcher  after  optical  facts,  which  in  the  aggregate 
constitute  optical  knowledge,  will  first  learn  the  A,  B,  C  of 
light  and  lenses,  together  with  the  reduction  and  transposition 
of  the  latter,  and  next  he  will  master  physiologic  optics,  in  addi- 
tion to  the  art  of  subjectively  correcting  with  lenses  any  mani- 
fest conditions  which  may  be  met.  The  student  may  then  be 
said  to  possess  sufficient  optical  knowledge  to  begin  the  study  of 
ocular  skiametry  with  a  fair  chance  of  achieving  success. 

DIFFICULTIES  TO  OVERCOME.  The  stumbling 
blocks  in  ocular  skiametry  are  not  few,  and  they  seem  to  grow 
apace  as  the  system  becomes  perfected  in  its  many  details.  The 
first  great  obstacle  which  usually  presents  itself  is  place,  or 
examination  room.  The  medical  refractionist  who  takes  up 
this  work  may  already  be  provided  with  a  regulation  dark- 
room for  his  ophthalmoscopic  work,  and  in  this  room  he  at- 
tempts to  practice  successful  skiametry.  The  conditions  being 
poor,  he  gets  poor  results  and  abandons  the  work  in  the  belief 
that  shadow  testing  is  sadly  overrated. 

The  non-medical  refractionist  may  possibly  go  to  the  other 
extreme.  The  specious  plea  that  a  dark  room  is  unnecessary 
is  listened  to,  then  not  being  able  to  use  a  cycloplegic,  and 
having  a  knowledge  of  the  static  method  only,  he  wonders  why 
his  skiametric  work  varies  so  with  his  trial  case  findings.    And 


22  DIFFICULTIES    TO    OVERCOME 

then,  too,  because  he  possesses  a  sufficient  degree  of  skill  to  feel 
comparatively  sure  of  the  action  of  the  shadow  in  an  occasional 
case,  he  either  blames  the  system  or  virtually  condemns  it  by 
faint  praise. 

Next  to  a  poorly-arranged  examination  room  in  point  of  dis- 
couragement with  shadow-testing  comes  an  inadequate  source  of 
illumination.  Almost  any  lamp,  whether  electric,  gas  or  oil, 
looks  to  a  novice  as  though  it  ought  to  prove  of  sufficient  in- 
tensity to  determine  a  shadow's  action,  because  when  the  Hght 
is  reflected  into  a  naked  eye  the  fundus  reflex  seems  fairly 
bright,  but  by  placing  a  lens  or  two  in  front  of  this  eye,  or  by 
permitting  the  patient  to  look  in  an  unfavorable  direction,  such  a 
pronounced  diminution  will  often  be  produced,  in  the  definition 
of  the  shadow,  as  to  render  accurate  work  impossible. 

Even  where  the  source  of  illumination  is  fifty-candle  power, 
or  more,  the  experienced  examiner  will  meet  with  cases  where 
the  deeply  pigmented  retina  gives  back  so  poor  a  reflection  that 
only  the  greatest  care  and  skill  can  determine  the  action  of  the 
shadow. 

There  is  a  vast  difference  in  general  illuminating  power 
between  a  flame  that  is  hooded  so  as  to  show  only  a  small 
aperture  and  one  that  is  not,  for  a  dark-room  light  to  be  satis- 
factory must  not  be  too  large.  Its  apparent  intensity  should 
resemble  the  "glory-hole"  of  a  furnace,  and  then  if  this  should 
prove  too  bright  for  an  occasional  supersensitive  eye  it  can 
always  be  diminished  by  moving  the  patient  farther  away 
from  it. 

The  law  that  light  decreases  in  proportion  to  the  square  of 
the  distance  at  which  it  is  used,  enables  a  light  intensity  equal 
to  sixty-candle  power  at  two  feet  away  to  be  decreased  to  fifteen- 
candle  power  by  withdrawing  to  a  distance  of  four  feet.  Thus 
it  will  be  seen  that  with  a  powerful  source  of  illumination  an 
examiner  can  readily  reduce  it  to  almost  any  candle  power  he 
desires. 


DIFFICULTIES    TO    OVERCOME  2^ 

Just  how  high  a  candle  power  the  human  eye  can  bear  with- 
out doing  it  injury  varies,  undoubtedly,  with  individuals  and 
the  duration  of  the  exposure.  A  hundred-candle  power  lamp 
hooded  so  that  only  a  limited  portion  of  its  general  radiant 
energy  is  available  could  probably  be  comfortably  borne  by  the 
average  eye  under  ordinary  skiametric  conditions  for  several 
minutes,  whereas  the  length  of  time  for  a  proper  measurement 
is  only  a  matter  of  seconds.  Too  bright  a  light  therefore  need 
not  be  feared  when  the  patient  does  not  look  directly  at  the 
reflection  in  the  mirror. 

In  using  a  bright  light,  however,  there  is  one  thing  an 
examiner  should  always  remember,  as  it  can  properly  be  classi- 
fied among  the  stumbling  blocks  to  be  avoided,  and  that  is  to 
never  allow  himself  to  look  directly  at  the  source  of  his  illumina- 
.tion  prior  to  or  during  an  examination.  The  reason  is  that  the 
sensitiveness  of  his  own  retina  is  such  as  to  retain  the  im- 
pressions made  by  a  bright  light  to  such  a  degree  that  duller 
objects  cannot  be  clearly  seen  for  several  minutes  thereafter, 
and,  as  a  consequence,  if  an  examiner  permits  himself  to  look 
directly  at  his  lamp  for  an  instant  or  two  and  then  tries  to  use 
his  mirror  he  will  find  it  very  difficult  to  detect  the  dull  outline 
of  the  shadow,  or  note  its  action.  If  an  inspection  of  a  lamp  is 
necessary  to  determine  its  condition,  or  distance  away,  it  is  a 
wise  examiner  who  will  derive  his  information  by  looking  a  few 
jnches  to  one  side  of  the  flame  and  not  directly  at  it. 

Another  stumbling  block  in  the  road  to  skiametric  success 
lies  in  corroded,  soiled  and  dusty  mirrors,  especially  at  the  edge 
of  the  so-called  "peep-hole"  of  the  skiascope.  Every  examiner 
should  possess  at  least  two  or  more  of  these  instruments,  so 
when  one  gets  out  of  order  it  can  be  sent  to  the  factory  for  re- 
silvering.  Mirrors,  to  give  the  best  service,  must  not  be  of  too 
great  a  diameter,  nor  must  their  peep-holes  be  large  or  bored 
through  the  glass.  Consequently  these  peep-holes,  which  are 
really  not  holes  in  the  strict  sense  of  the  word,  but  round  spots 


24  DIFFICULTIES    TO    OVERCOME 

of  clear  glass,  made  by  scraping  off  the  silver  of  the  mirror,  must 
be  kept  immaculately  clean  so  as  to  prevent  particles  of  dust 
from  interfering  with  the  free  passage  of  light,  or  else  the 
shadow's  action  will  be  perceptibly  dimmed. 

One  of  the  underlying  causes  of  the  success  achieved  in 
many  branches  of  modern  science  is  undoubtedly  due  to  ultra- 
cleanliness  and  attention  to  details,  and  so  it  will  be  with 
advanced  optometry  as  regards  details,  for  dealings  with  imag- 
inary quantities  of  elastic  ether,  as  light  is  termed,  call  for 
extreme  care  on  the  part  of  the  examiner,  if  he  is  of  the  kind 
that  will  be  satisfied  with  nothing  short  of  the  highest  attain- 
ment. 

A  thorough  knowledge  of  lenses  is  still  another  important 
factor,  as  there  is  probably  no  one  study  connected  with  a  skia- 
metrist's  educational  equipment  which  demands  a  more  perfect 
mastery  than  does  that  of  the  reducing,  transposing  and  com- 
bining lens  values.  In  his  desire  to  attain  perfection  on  the 
practical  side  of  adapting  glasses  to  the  eyes  of  others,  the  stud- 
ent is  apt  to  pass  hurriedly  by  the  dry  underlying  optical  prin- 
ciples upon  which  lenses  are  based  and,  as  a  consequence,  after 
his  first  few  years  of  "success  in  every  case"  his  desire  to  climb 
higher  is  interfered  with  through  his  lack  of  knowledge  of  that 
which  he  ought  to  have  learned  at  the  beginning  of  his  optical 
career. 

In  ocular  skiametry  a  simple  stumbling  block  to  many 
students  is  their  inability  to  tell  what  the  true  refraction  of  their 
patient's  eye  is,  when  it  takes  an  ordinary  lens  quantity  of,  say, 
one  diopter  to  reverse  the  shadow  in  one  meridian,  while  only  a 
half-diopter  is  required  to  reverse  it  in  the  meridian  at  right 
angles  to  this.  Especially  is  this  true  where  the  axes  happen  to 
be  oblique,  or  where  one  lens  is  plus  and  the  other  minus. 

Now  this  is  all  wrong,  for  if  an  optometrist  ought  to  know 
anything  he  ought  to  know  all  about  lenses — how  they  are  made, 
what  index  of  refraction  and  spherical  aberration  mean,  wherein 


DIFFICULTIES   TO   OVERCOME  25 

cylindrical,  spherical  and  ellipsoidal  curvatures  differ  and,  above 
all,  the  very  best  way  to  combine  lens  quantities  in  order  to 
produce  the  highest  degree  of  central  and  peripheral  vision, 
together  with  angle  and  decentration  for  the  relief  of  strain  and 
the  production  of  comfort. 

_A  thorough  knowledge  of  light  and  lenses  is  the  great  key 
to  the  achievement  of  skiametric  success.  After  a  student  has 
learned  all  about  the  physical  side  of  refractive  work  the  phys- 
iologic becomes  easier,  just  as  a  mathematician  who  has  skipped 
some  fundamental  principle  finds  his  higher  work  puzzling,  but 
where  he  has  covered  his  ground  carefully  then  his  advance- 
ment is  less  difficult. 

A  very  few  sittings  will  give  a  student  the  mastery  of  a 
skiascopic  mirror  and  enable  him  to  tell  the  movement  of  the 
pupillary  shadows,  but  how  to  control  these  shadows  by  the  aid 
of  lenses  combined  with  fixation,  and  to  know  the  real  optical 
value  of  the  refractive  power  used,  is  where  one  of  the  greatest 
of  the  stumbling  blocks  in  shadow  testing  lurks,  so  that  those 
who  become  discouraged  in  their  skiametric  efforts  must  not 
blame  this  grand  test,  but  look,  rather,  to  their  own  weakness  in 
their  lack  of  adequate  optical  knowledge  and  skill. 

There  is  one  more  point  to  which  attention  should  be  di- 
rected, although  it  can  hardly  be  called  a  "stumbling  block," 
even  though  in  some  cases  it  seems  to  act  as  such.  It  pertains 
to  an  examiner's  own  vision,  which  should  be  such  as  to  enable 
him  to  see  with  definition  a  moderately  pale  shadow  on  a  pink 
background  at  a  distance  of  at  least  forty  inches.  Therefore  all 
examiners  having  myopia,  should  have  their  own  refractive 
errors  corrected  to  within  less  than  one  diopter  before  they 
attempt  skiametric  work.  All  hypermetropes,  on  the  other  hand, 
whose  amplitude  of  accommodation  at  thirteen  inches  is  less  than 
their  error  of  refraction  must  also  wear  their  correcting  lenses 
before  they  can  make  satisfactory  shadow  tests,  and  this  applies, 
too,  to  presbyopes  who  should  wear  their  reading  correction 


26  DIFFICULTIES  TO  OVERCOME 

when  using  the  mirror  at  near  points.  It  would  seem, 
however,  that  the  peep-hole  in  a  skiascope  ought  to  act  as  a 
pinhole  test  and  give  an  examiner  good  vision  no  matter  what 
his  refractive  error  might  be,  but  experience,  that  great  teacher, 
rules  it  otherwise  in  those  cases  where  high-class  results  are 
sought  for. 

Some  examiners  have  found  difficulty  in  keeping  the  peep- 
hole of  a  skiascope  exactly  in  front  of  their  fixing  eye,  and  thus 
obtaining  a  good  reflex.  This  is  usually  due  to  their  inability  to 
close  the  unused  eye,  hence  practice  in  this  respect  is  important, 
for  if  one  eye  is  in  use  the  other  should  be  occasionally  closed 
in  order  to  make  sure  that  the  fixing  eye  is  properly  located. 


CHAPTER  II. 

Proper  and  Improper  Examination  Rooms. — Size^  Inten- 
sity AND  Control  of  Illumination. — The  Plane  Ski- 
ascope, How  to  Handle  It,  and  Some  Novel  Inven- 
tions. 

EXAMINATION  ROOMS.  Since  the  fitting  of  glasses 
"over  the  counter"  has  practically  passed  away,  the  considera- 
tion of  where  the  fitting  should  be  done  is  now  in  order. 

To  describe  an  ideal  examination  room  is  quite  a  different 
matter  than  it  is  to  attempt  the  description  of  an  adequate  apart- 
ment that  might  serve  fairly  well  as  a  place  in  which  to  prac- 
tice ocular  skiametry. 

The  complaint  which  is  frequently  heard  from  many  who 
attempt  to  do  refraction  work  without  having  suitable  place  and 
apparatus  is  that  they  lack  the  requisite  space,  whereas  an 
examination  of  the  store  or  office  by  one  experienced  as  to  re- 
quirements might  lead  to  the  discovery  of  quite  a  number  of 
places  which  could  be  rendered  available  by  the  use  of  properly 
strung  wires  for  hanging  light-proof  curtains,  and  which  .could 
also  be  made  decorative  in  appearance.  Then,  too,  many  are 
persuaded  that  an  examination  room  must  be  of  Egyptian  dark- 
ness, without  ventilation,  where  both  examiner  and  patient  will 
be  very  uncomfortable,  especially  during  warm  weather. 

Now  this  is  a  wrong  conception.  An  adequate  examina- 
tion room  needs  to  be  of  only  semi-darkness,  in  fact  if  it  is  just 
light  enough  to  make  the  headlines  of  an  ordinary  newspaper 
discernible  at  midday  it  will  be  found  dark  enough  for  all  opto- 
metric  purposes.  The  "Mahomet  and  the  mountan"  principle 
can  be  made  use  of  by  increasing  the  intensity  of  the  light 


28  EXAMINATION    ROOMS 

source,  instead  of  making  the  room  appear  as  dark  and  gloomy 
as  the  interior  of  a  hearse. 

The  space  occupied  need  not  be  very  wide.  The  length  of 
room,  however,  ought  to  be  at  least  twenty  feet,  but  where  this 
distance  cannot  be  obtained  a  length  of  ten  feet  can  be  made  to 
appear  as  twenty  by  the  use  of  an  ordinary  wall  mirror,  test 
cards  with  reversed  letters  being  placed  over  the  head  of  the 
patient  in  a  position  where  their  reflection  can  readily  be  seen  in 
the  mirror. 

The  ventilation  should  be  perfect,  and  the  space  ought  to 
contain  several  chairs  for  the  use  of  those  who  accompany  the 
patient,  while  the  surroundings  should  be  made  as  cheerful  as 
possible  by  means  of  rugs,  pictures,  etc. 

Both  objective  and  subjective  tests  should  be  used  without 
having  to  move  the  patient  from  the  chair  in  which  he  is  first 
seated,  it  being  better  to  bring  all  instruments  and  devices  to  the 
patient  rather  than  require  the  patient  to  go  to  them. 

First  impressions  are  said  to  be  lasting,  so  that  if  patients 
are  shown  into  apartments  that  look  as  though  they  were  in- 
tended for  optometric  purposes  their  confidence  is  more  than 
half  won. 

There  is  a  fitness  of  things,  and  those  whose  practice  is  in 
accord  with  this  "fitness"  generally  have  occasion  to  feel  satis- 
fied with  the  results  obtained  from  having  given  attention  to  the 
details  of  environment.  Indeed,  it  has  already  been  said  by 
many  that  next  to  professional  knowledge  and  skill  a  well 
appointed  examination  room  is  the  very  best  kind  of  an  adver- 
tisement an  optometrist  can  have. 

SOURCES  OF  ILLUMINATION.  The  reader's  atten- 
tion is  called  to  the  importance  of  using  a  proper  source  of 
illumination  in  order  to  succeed  in  shadow  testing.  Therefore 
it  will  be  the  purpose  here  to  describe,  with  the  assistance  of 
drawings  and  photo-reproductions,  some  of  the  various  lamps 


SOURCES  OF  ILLUMINATION  29 

employed  for  this  purpose,  and  to  offer  criticisms  regarding  the 
advantages  and  disadvantages  consequent  upon  their  use. 

Practising  skiametry  by  means  of  a  schematic  eye  is  very 
easy  in  comparison  to  practising  it  upon  a  living  eye,  for  with 
a  model  eye  almost  any  kind  of  light  will  answer,  but  not  so 
with  the  living  organ  where  the  light  source  should  resemble  the 
glow  emanating  from  the  "glory-hole"  of  a  furnace. 

Oil  lamps  of  all  types,  while  many  are  magnificent  for  gen- 
eral lighting  purposes,  fall  away  below  the  standard  of  efificiency 
when  employed  for  general  skiametric  uses.  The  draught  in 
almost  all  lamps  is  an  important  factor,  and  as  metal  chimneys 
cannot  be  easily  made  to  take  the  place  of  glass  ones,  on  account 
of  the  transparent  aperture  which  is  required  opposite  the 
flame,  it  has  been  found  necessary  to  either  line  or  cover  all 
glass  chimneys  with  an  opaque  substance  which  extreme  heat 
cannot  affect.  But  even  where  the  chimney  is  lined  with  a  white 
pigment  it  still  falls  short  of  giving  satisfaction  as  an  efficient 
illuminator,  although  the  maker  may  claim  that  his  lamp  has 
a  general  efficiency  of  over  one  hundred-candle  power. 

The  reason  for  the  shortcomings  of  oil  lamps,  even  those 
using  a  so-called  "flame  spreader,"  is  due,  no  doubt,  to  the  fact 
that  the  flame,  though  large,  is  apt  to  be  very  low,  and  when 
its  general  intensity  is  hooded  down  to  the  size  of  a  two  or 
three  centimeter  aperture,  which  is  necessary  in  order  to  obtain 
good  results  with  a  plane  mirror,  the  flame  is  found  of  insuf- 
ficient brightness  to  meet  an  examiner's  needs. 

Perhaps  some  day  some  inventive  mind  will  devise  a  con- 
densing reflector  which  will  permit  of  hooding  the  light  of  oil 
lamps  down  to  a  small  aperture  and  at  the  same  time  obtain  the 
requisite  intensity  of  illumination,  but  as  yet  this  has  not  been 
achieved. 

Next  to  oil  comes  gas.  And  here  the  field  of  illumination 
broadens,  thanks  to  the  inventors  of  the  "Argand"  and  "Wels- 
bach"  burners,  and  to  the  gas-generating  qualities  of  naphtha 


30 


SOURCES  OF  ILLUMINATION 


and  of  acetylene.  Ranking  above  oil  burners  comes  the  Argand 
gas  lamp,  which  also  requires  a  draught  to  make  it  burn  prop- 
erly, hence  a  glass  chimney  is  necessary  for  its  use. 

But  while  the  Argand  gas  lamp  is  vastly  superior  to  oil 
lamps  in  general,  it  is  still  somewhat  below  the  required  stand- 
ard of  efficiency,  even  when  working  at  its  best.  The  flame  has 
a  yellowish  white  appearance  and  seems,  like  the  flame  of  an  oil 

Fig.  3. 


ACETYLENE  GAS  LAMP  WITH   METAL  CHIMNEY. 

lamp,  to  lack  the  illuminating  energy  necessary  to  meet  modern 
skiametric  needs,  although  in  favorable  cases  fair  work  can 
sometimes  be  done  by  its  aid. 

Acetylene  lamps  represent  another  style  of  gas  burners  which 
in  point  of  intensity  of  illumination  can  probably  hold  their  own 
against  all  competitors.  The  style  shown  in  Fig.  3  represents  a 
portable  type. 


SOURCES  OF  ILLUMINATION 


31 


This  lamp  is  similar  in  appearance  to  an  ordinary  table  lamp, 
with  the  exception  that  it  has  an  asbestos  lined  metal  chimney. 
It  is  commercially  named  an  "Electrolite  gas  lamp,"  and  uses 
pulverized  calcium  carbide.  Its  use  is  endorsed  by  the  board  of 
fire  underwriters,  and  it  is  easy  to  care  for.  The  light  it  gives 
is  over  fifty-candle  power,  while  the  expense  of  maintaining  it  is 
only  about  one  cent  an  hour. 

Fig.  4. 


ASBESTOS  LINED  METAL  CHIMNEY. 


Skiametrists  are  certainly  to  be  congratulated  on  the  inven- 
tion of  this  lamp,  especially  those  who  are  compelled  to  do  work 
away  from  their  properly  appointed  examination  rooms,  for  as 
a  portable  lamp  it  is  very  satisfactory. 

In  point  of  brilliancy,  reliability,  cost  of  maintenance  and 
ease  of  adjustment,  however,  no  gas  lamp  is  superior  to  the 


32 


SOURCES  OF  ILLUMINATION 


Welsbach  type,  especially  with  a  metal  asbestos  lined  chimney, 
as  shown  in  Fi^.  4. 

This  burner  is  of  the  "Incandescent"  kind  wherein  chimney 
draught,  as  with  oil  burners,  is  not  so  much  of  a  factor.  A  glass 
chimney,  however,  gives  better  results  than  a  metal  one  does,  due 
to  the  fact  that  the  light  aperture  is  covered,  thus  preventing  an 
inrush  of  air  which  can  interfere  with  the  white  heat  of  the 

Fig.  5. 


O 


ASBESTOS  LINED  GLASS  CHIMNEY. 


mantle.  Figs.  4  and  5  show  two  patterns  of  chimneys,  one  metal 
and  the  other  glass,  which  can  be  used  on  the  same  style  of 
burner. 

The  Fig.  5  chimney  being  further  away  from  the  mantle,  the 
sides  do  not  get  as  hot  as  in  the  pattern  shown  in  Fig.  4,  which 
is  made  in  both  glass  and  metal.  But  the  smaller  the  chimney 
the  more  convenient  is  the  adjustment  of  the  light,  the  source  of 


SOURCES  OF  ILLUMINATION 


33 


illumination  being  nearer  to  the  surface,  tiierefore  Fig.  4  is  to  be 
preferred. 

In  Fig.  6  is  shown  an  asbestos  paper  chimney  cover,  with 
iris  diaphragm  opening.  This  cover  can  be  used  outside  of  an 
ordinary  glass  chimney,  and  serves  the  purpose  of  a  light  screen 
very  well,  although  it  has  the  faults  of  the  chimney  shown  in 

Fig.  6. 


ASBESTOS   PAPER   CHIMNEY    COVER   WITH    IRIS   DIAPHRAGM 
OPENING. 


Fig.  5  as  to  size.  The  iris  diaphragm,  also,  seems  to  be  an 
unnecessary  arrangement,  for  it  is  the  size  of  the  skiascopic 
mirror  that  regulates  the  facial  area  of  illumination  and  not 
the  size  of  the  chimney  aperture,  unless  a  condensing  lens  is 
used,  which  would  indeed  be  troublesome. 

The  Welsbach  lamp  gives  an  ideal  light  for  shadow  testing, 


34  SOURCES  OF  ILLUMINATION 

as  its  flame  is  bluish-white,  while  its  intensity  is  ample,  espe- 
cially when  its  mantle  is  evenly  heated  to  incandescence.  The 
one  unfavorable  criticism  which  can  be  made  regarding  it  is  the 
fragile  character  of  its  mantles,  which  are  easily  injured  or  de- 
stroyed. But  fortuna-tely  these  mantles  are  inexpensive  and  are 
not  difficult  of  adjustment. 

In  connection  with  naphtha,  or  gasolene,  the  Welsbach 
burner  can  also  be  used,  but  while  the  light  obtained  is  not 
as  satisfactory  as  where  so-called  "City"  gas  is  employed,  yet 
the  results  secured  are  vastly  superior  to  the  use  of  oil.  The 
general  use  of  gasolene  has  its  disadvantages,  resulting  from  its 
explosive  qualities.     This  is  a  question,  however,  on  which  the 

Fig.  7. 


SPIRAL  FILAMENT  IN  ELECTRIC  LAMP. 

makers  of  gasolene  lamps  and  the  fire  insurance  companies  are 
not  at  all  in  accord.  But  as  efficient  illuminators  for  skiametric 
uses,  gasolene  lamps,  using  the  Welsbach  type  of  burners,  will 
be  found  more  satisfactory  than  oil,  provided  they  are  kept  in 
perfect  order. 

Wood  alcohol  is  now  being  extensively  used  for  lighting  and 
heating,  so  there  is  every  reason  to  believe  that  lamps  suitable 
for  optometric  purposes  will  soon  be  devised  where  this  illumi- 
nant  can  be  employed. 

Electric  lamps  of  the  general  house-lighting  variety,  with 
long  carbon  filaments,  are  perhaps  among  the  most  unsatisfac- 
tory of  all  illuminators  for  use  in  connection  with  ocular  ski- 


SOURCES  OF  ILLUMINATION  35 

ametry,  no  matter  whether  the  glass  bulbs  are  of  the  clear  or 
the  frosted  variety. 

An  electric  lamp,  to  be  of  service  in  this  work,  must  have 
its  filament  in  compact  form,  similar  in  shape  to  the  coils  of  a 
watch  hairspring.  Then  the  light  energy  of  the  carbon  wires 
when  heated  to  incandescence  can  be  concentrated,  and  the 
results  obtained  made  superior  to  the  mantle  type  of  gas  lamp. 
Fig.  7  shows  an  electric  lamp  filament  of  the  spiral  kind  referred 
to.  This  lamp  needs  to  be  handled  with  great  care,  since  owing 
to  the  size  and  brittle  character  of  its  filament  it  becomes  easily 
broken  by  a  sudden  jar,  or  through  rough  handling  in  the  mail, 
or  when  shipped  by  express. 

Fig.  8  shows  this  same  lamp  with  its  glass  bulb  coated  with 
a  thick  asbestos  pigment,  leaving  a  one-inch  aperture  in  its  side 
through  which  the  light  can  emerge. 

This  lamp  is  rated  at  fifty-candle  power  and  gives  a  mag- 
nificent reddish  white  light.  The  white  hot  filament,  or  carbon 
wires,  generate  considerable  heat  which,  of  course,  will  melt 
the  rubber  or  composition  socket  handle  if  the  lamp  happens  to 
be  used  upside  down.  The  heat  from  one  of  these  lamps  has 
been  known  to  char  the  curtain  hangings  of  a  window,  with 
which  it  came  in  contact.  But  used  as  it  is  intended  to  be  used, 
this  style  of  lamp  certainly  supplies  an  adequate  illumination  for 
any  kind  of  examination  room,  whether  light  or  dark,  or  where 
gas  cannot  be  obtained,  such  as  in  modern  office  buildings,  but 
once  used,  an  examiner  is  rarely  ever  satisfied  with  any  other 
form  of  lamp.  Most  high  candle-power  lamps,  however,  are 
somewhat  expensive  and  burn  out  easily,  they  should  therefore 
never  be  burned  for  long  periods  of  time  but  be  turned  off  and 
allowed  to  cool  as  frequently  as  possible.  A  snap  switch  in 
place  of  the  ordinary  socket  key  should  be  used,  and  a  lamp 
ought  never  to  be  burned  on  a  current  that  is  of  a  higher  voltage 
than  that  for  which  the  lamp  is  made. 

Attention  to  these  details  will  often  prolong  the  life  and  serv- 


36 


SOURCES  OF  ILLUMINATION 


ice  of  a  lamj)  two  or  three- fold,  for  when  the  inside  of  the 
lamp  bulb  shows  a  reddish  deposit  on  the  glass  it  indicates  de- 
composition of  the  carbon  filament,  due  to  overuse,  or  abuse  of 
some  kind. 

Fic.  8. 


AUTHOR  S     ASBESTOS     COVERED     ELECTRIC     LAMP. 

The  cost  of  maintenance  of  an  electric  lamp,  too,  is  some- 
what higher  than  the  mantle-type  of  gas  lamp,  and  its  durability 
is  not  as  great.  Any  increase  in  current,  even  of  only  a  few 
volts,  such  as  frequently  occurs  in  cities  where  it  is  intensified 
at  sundown,  serves  to  shorten  the  life  of  a  lamp  very  mate- 
rially. These  uncertainties  of  current  can  be  controlled  by  what 
are  called  resistance  attachments,  or  rheostats,  if  an  examiner 
cares  to  incur  the  expense.  The  superior  light  given  by  these 
high  candle-power  electric  lamps,  however,  more  than  com- 
pensates for  the  trouble  and  expenditure  their  use  entails. 

Another  form  of  electric  illumination,  and  one  which  has  the 
added  advantage  of  portability,  is  the  combined  lamp  and  mir- 
ror, known  as  the  luminous  type  of  retinoscope.  Fig.  9  illus- 
trates the  appearance  of  a  late  model  of  one  of  these  instru- 
ments, for  which  the  makers  put  forth  the  following  claims : 


SOURCES  OF  ILLUMINATION 


Z7 


"This  self-contained  Electric  Retinoscope, 
combining  as  it  does  the  battery,  lamp,  mir- 
ror and  illuminated  fixation  letters,  leaves 
nothing  to  be  desired  in  an  instrument  of 
this  kind.  It  offers  tremendous  advantages 
in  every  branch  of  Retinoscopy.  It  can  be 
used  in  any  place  or  position  irrespective  of 
circumstances. 

"The  Jumbo  Handle  Battery  shown  is 
designed  to  meet  the  demand  for  a  very 
compact  and  portable  instrument  of  maxi- 
mum endurance.  It  is  made  of  aluminum 
and  is  designed  to  hold  a  two-cell  battery  of 
regular  stock  size.  This  handle  is  well  pro- 
portioned, is  convenient  to  hold  and  has  a 
compressible  circuit  breaker  conveniently 
located  for  the  thumb  of  the  operator.  It 
is  arranged  for  either  a  touch  or  a  fixed 
contact,  the  lamp  being  lighted  either  by 
pressing  the  extending  arm  against  the 
handle  or  swinging  it  around  in  contact  with 
the  clip  on  the  top  of  the  cap  as  desired. 

"The  Illuminated  Fixation  Letters,  ap- 
pearing to  the  left  of  the  mirror,  are  invalu- 
able in  the  Dynamic  System  of  Skiascopy. 

"They  are  clearly  cut  in  white  against  a 
black  background,  and  being  located  in  close 
proximity  to  the  mirror,  the  refraction  can- 
be  estimated  almost  at  the  macula.  These 
letters  are  rendered  visible  in  the  dark  room 
by  a  divergent  shaft  of  light  which  passes 
through  an  opening  in  the  tube  containing 
the  lamp,  which  illuminates  the  mirror.  This 
coincident    illumination    of   the    mirror    and 


Fig.  9. 


DE  ZENG  electric 
RETINOSCOPE. 


38 


SOURCES  OF  ILLUMINATION 


fixation  letters  obviates  the  necessity  of  any  extraneous  light, 
thereby  affording  the  operator  the  advantage  of  a  perfectly 
darkened  room  when  so  desired." 

The  lamp  used  is  of  only  one  or  two-candle  power  and  is 
located  behind,  and  close  to,  a  strong  convex  lens,  which  serves 
to  parallel  the  light  radiation  and  thereby  avoid  any  waste  due 
to  this  cause,  but  like  other  electric  lamps  it,  too,  is  sensitive  to 
abuse. 

The  light  it  gives  is  a  fairly  intense  one  and  enables  good 
work  to  be  accomplished  by  those  who  are  acquainted  with  its 

Fig.  id. 


THE  "hardy"  W^ALL  BRACKET  FOR  GAS  OR  ELECTRIC  LAMP. 


peculiarities.  For  dynamic  work  its  fixation  letters  are  limited 
in  both  numbers  and  position. 

As  a  portable  light  it  is  compact  and  easy  of  transportation 
and,  in  an  emergency,  serves  the  purpose  of  being  useful  as  an 
ophthalmoscope  as  well. 

A  point  to  bear  in  mind  in  connection  with  adequate  illumin- 
ation in  skiametric  work  is  to  have  whatever  lamp  may  be  used 
so  arranged  that  its  adjustments,  forward  and  backward  to  and 
from  an  examiner's  own  eye,  are  readily  obtainable.  The  adjust- 
ment as  to  height  is  not  so  important  as  long  as  the  light  is 


VARIOUS  SKIASCOPES  39 

about  level  with  the  patient's  head  and  is  situated  from  six  to 
twelve  inches  to  the  patient's  right.  The  alterable  distance  for- 
ward and  backward  is,  however,  quite  essential,  as  it  enables 
the  intensity  of  illlimination  to  be  controlled  by  an  examiner  as 
his  case  demands.  A  very  simple  way  to  arrange  for  this  is  to 
use  a  wall  bracket  similar  to  the  one  shown  in  Fig.  lo. 

This  bracket  is  arranged  for  gas  and  electricity,  and  thus 
gives  an  examiner  a  double  system  of  illumination  which,  in 
case  of  necessity,  may  prove  of  very  great  value  in  preventing  a 
break-down. 

In  summing  up  the  question  of  illumination,  perhaps  the 
expression  from  the  pen  of  a  western  specialist  will  serve  to 
state  the  case  fairly  well.  He  wrote,  "I  fully  realize  that 
proper  illumination  is  the  foundation  of  success  in  skiametry." 
And  it  may  be  added  that  this  opinion  is  shared  by  many 
others  who  have  had  experience. 

VARIOUS  SKIASCOPES.  The  confusion  following  the 
use  of  two  forms  of  skiascopes,  such  as  those  having  plane  and 
those  having  concave  mirrors,  has  led  to  the  virtual  abandon- 
ment of  the  latter  by  most  of  the  skiametrists  of  the  country. 
There  are  possibly  some  conditions  under  which  a  concave  re- 
flector might  give  an  examiner  better  service  than  a  plane 
one  would,  but  these  are  rare,  and  for  general  all-round  skia- 
metric  purposes  the  plane  mirror  is  to  be  greatly  preferred.  All 
mirrors  should  be  as  brilliantly  silvered  as  possible,  and  the 
reflections  from  them  ought  to  be  perfectly  round  and  free  from 
distortion. 

Regarding  the  size  or  working  part  of  a  mirror,  this  can  be 
easily  determined  by  holding  it  at  the  maximum  distance  at 
which  it  is  to  be  used  and  covering  its  periphery  with  washer- 
like pieces  of  paper.  The  size  of  the  reflecting  surface  neces- 
sary to  produce  the  best  results  while  in  actual  service  can  then 


40  VARIOUS  SKIASCOPES 

be  noted.  This  will  usually  be  found  to  represent  an  area  of 
about  three-quarters  of  an  inch  in  diameter. 

The  central  aperture,  or  peep-hole,  should  be  as  small  as 
possible  and  yet  permit  of  acute  vision  on  the  part  of  the 
examiner.  A  diameter  of  one  or  two  millimeters  is  generally 
sufficient  for  the  purpose.  Having  the  handle  at  least  six  inches 
long  will  be  found  especially  advantageous  in  using  body  move- 
ments. 

Keeping  the  peep-hole  free  from  dust  and  dirt  is  also  im- 
portant. A  frequent  twist  of  the  skiascope  just  before  it  is 
used,  and  while  its  front  and  back  are  covered  with  a  handker- 

FlG.    II. 


A  SIMPLE  SKIASCOPE. 

chief  held  between  the  thumb  and  forefinger  of  the  operator's 
hand,  is  usually  all  that  is  necessary  in  order  to  keep  it  quite 
clean. 

Fig.  II  represents  the  skiascope  generally  employed  in  the 
practice  of  what  is  usually  called  "retinoscopy,"  where  accom- 
modation is  supposed  to  be  relaxed  by  having  the  patient  look 
over  the  examiner's  shoulder,  or  where  "a  reliable  cycloplegic" 
has  been  used. 

As  will  be  seen  in  subsequent  chapters,  the  use  of  cards  for 
fixing  the  vision  of  the  patient  at  the  same  distance  away  as  that 


VARIOUS  SKIASCOPES 


41 


at  which  the  mirror  is  operated  renders  some  means  for  attach- 
ing cards  to  the  skiascope  almost  a  necessity.  Fig.  12  shows  a 
device  to  which  the  name  "Double  Bracket  Skiascope"  has  been 

Fig.  12. 


AUTHOR  S    DOUBLE    BRACKET    SKIASCOPE. 


given.  The  lenses  in  the  disc  at  the  back  of  this  skiascope 
contain  plus  spherics  of  i.  D,  1.50  D.  2.  D.  2.50  D.  3.D.  4.D.  and 
5.   D.    for  the  purpose  of  correcting  any  presbyopia   that  an 


42  VARIOUS  SKIASCOPES 

optometrist  may  have,  himself,  while  working  at  any  distance 
less  than  forty  inches,  so  as  to  obtain  a  clear  view  of  the  action 
of  the  shadow.  When  an  examiner  is  under  forty-five  years 
of  age  the  use  of  this  lens  disc  is  seldom  required. 

The  arrangement  of  the  brackets  attached  to  the  mirror 
frame  are  such  that  the  cards  can  be  given  a  number  of  adjust- 
ments to  suit  possible  contingencies.  Also  for  the  purpose  of 
maintaining  fixation  so  it  can  be  relied  upon,  for  variation  in 
fixation  means,  of  course,  an  alteration  in  the  patient's  refrac- 
tion. The  usual  procedure  is  for  the  examiner  to  request  that 
the  irregularly  placed  letters  on  the  fixation  card.  Fig.  13,  be 

Fig.  13.  Fig.  14. 


SKIAMETRIC   FIXATION    CARDS. 

counted  by  the  patient.  Then,  if  this  does  not  prolong  the  fixa- 
tion period  sufficiently,  the  request  is  made  to  state  what  letters 
of  the  alphabet  are  missing,  or  what  letters  appear  more  than 
once. 

If  the  visual  angle  needs  changing,  or  the  focal  fixation  re- 
quires slight  alteration,  then  the  other  fixation  card,  Fig.  14, 
can  be  made  use  of,  reliable  fixation  being  maintained  by  dis- 
puting the  patient's  count  of  the  dots.  The  position  of  the  Fig. 
13  card  also  has  an  advantage  in  its  being  placed  so  as  to  corre- 
spond with  the  examiner's  own  nodal  point.  When  the  light 
source  is  found  unpleasant  to  the  unused  eye  of  an  examiner  it 
may  be  obviated  by  having  card.  Fig.  14,  made  longer  and 
adjusted  so  as  to  act  as  a  screen. 


HANDLING  THE   PLANE   SKIASCOPE 


43 


HANDLING  THE  PLANE  SKIASCOPE.  Regarding 
the  proper  way  to  handle  a  skiascope,  the  various  tutors  in 
skiametry  differ,  but  all  agree  that  the  movements  of  the 
mirror  should  be  of  the  slow,  steady,  straight-line  order,  and 
as  free  from  wabbling  and  semi-circular  motions  as  possible. 
When  movements  of  the  mirror  are  attempted  by  the  hand- 

FiG.  15. 


^^^^^HHHKi^^^^^^^^^H 

^^IL&JB 

\m 

■'■  M 

^^^^           '■'    ^!, 

^^^B         ^  i'     ^"-^  - 

MANNER  OF   HOLDING   AUTHOR  S   SKIASCOPE. 


tilting  method  it  takes  many  years  of  practice  before  a  positive 
straight-line  motion  in  all  meridians  of  an  eye  can  be  depended 
upon.  But  where  the  movements  are  made  by  a  body-tilting 
method  the  mastery  of  the  mirror  is  very  rapid,  some  beginners 
acquiring  it  almost  perfectly  after  only  a  few  days  of  practice. 
A  description  of  this  body  method  is  as  follows :  The  mirror 
handle  is  to  be  grasped  near  its  lower  end,  when  the  skiascope  is 


44  HANDLING  THE  PLANE   SKIASCOPE 

held  in  a  vertical  position.  The  elbow  and  arm  of  the  hand 
holding  the  mirror  are  to  be  pressed  tightly  against  the  side  of 
the  body,  while  the  upper  and  inner  edge  of  the  metal  disc, 
upon  which  the  mirror  is  mounted,  is  to  be  held  firmly  against 
the  side  of  the  examiner's  nose  or  resting  on  the  eyebrow  in 
such  a  manner  that  the  peep-hole  of  the  mirror  is  exactly  in 
front  of  the  operator's  pupil.  With  the  mirror  handle  held  in  a 
rigid  manner,  almost  the  entire  body  is  made  to  assist  in  giving 
the  proper  movements.  The  examiner's  upper  torso,  or  trunk, 
acts  as  though  it  was  pivoted  at  the  waist,  while  the  neck  and 
heaving  chest  aid  in  the  necessary  motions.  To  say  that  this 
action  involves  a  sort  of  courtesy,  or  bowing  movement,  might 
perhaps  add  to  its  description.  Fig.  15  may  also  serve  to  give  a 
better  idea  of  how  the  skiascope  should  be  held. 

It  is  always  better  for  an  examiner  to  learn  to  work  with 
both  eyes  open  when  locating  the  reflected  light  on  the  face  of 
a  patient.  After  this  location,  the  eye  not  in  use  at  the  peep-hole 
should  be  closed,  so  as  to  stimulate  concentration  and  sharpen 
the  brightness  of  the  fundus  reflex,  as  well  as  to  define  the 
shadow's  edge.  The  closing  of  the  unused  eye  serves  to  obviate 
any  discomfort  an  examiner  may  experience,  caused  by  the 
glaring  light  from  the  lamp  in  use,  and  especially  so  if  the  latter 
is  at  close  range. 

The  mirror  light  on  the  patient's  face  ought  not  to  move 
over  an  inch  in  any  one  direction,  and  the  pink  pupil  should 
hardly  ever  be  allowed  to  pass  entirely  from  view  after  once 
being  found.  The  examiner  should  direct  his  attention  to  one 
edge  of  the  patient's  pupil  only,  as  in  this  way  he  can  quickly 
determine  whether  the  shadow  is  with  or  against  the  mirror's 
movement  in  any  one  meridian.  All  movements  should  also  be 
made  very  slowly,  since  rapidity  of  motion  often  interferes  with 
judgment  as  to  the  shadow's  action,  just  as  the  spokes  in  a 
wheel  are  found  to  be  more  difficult  to  count  when  the  wheel 
revolves  rapidly  than  when  it  goes  slowly. 


NOVEL  SKIASCOPES 


45 


NOVEL  SKIASCOPES.  Among  the  novel  devices  for 
shadow  seeing  can  be  mentioned  the  Reisner  "Retinoscope," 
shown  in  Fig.  i6. 

The  claims  for  this  instrument  are  set  forth  by  the  manu- 
facturers as  follows : 

Fig.  1 6. 


REISNER  S  RETINOSCOPE. 


"The  Reisner  Retinoscope  has  a  small  lever  for  tilting  the 
mirror  mechanically  with  self-recording  axis  on  back.  Tilting 
a  mirror  mechanically  instead  of  the  old  way  gives  a  positive 
movement  straight  across  the  meridian  being  neutralized, 
thereby  avoiding  the  circular  motion  common  with  the  ordinary 
mirror,  enabling  an  operator  to  determine  definitely  the  differ- 
ence between  a  case  of  conical  cornea  and  mixed  or  irregular 
astigmatism.     Referring  to  the  back  of  the   instrument,   the 


46 


NOVEL  SKIASCOPES 


number  indicated  by  pointer  represents  the  axis  at  which  lens 
should  be  placed  in  frame." 

Another  departure  in  retinoscopes  is  the  Klein  "Non-Irritat- 
ing Retinoscope,"  shown  in  Fig.  17. 

The  mirror  of  this  instrument  is  made  of  amber  glass  sil- 
vered and  mounted  in  the  usual  way.  The  makers  ask  the  fol- 
lowing pertinent  question : 


Fig 


KLEIN  S    RETINOSCOPE. 


"Why  continue  to  use  the  ordinary  white  glass  retinoscope, 
and  cause  needless  annoyance  to  your  patients,  when,  for  a 
little  more,  you  can  obtain  Klein's  Non-Irritating  amber  glass 
retinoscope?  This  instrument  is  monochromatic,  reduces  the 
actinic  rays,  insures  from  ten  to  tzventy  per  cent,  greater  dila- 
tion of  the  pupil  and  minimizes  the  diffused  rays,  which  are 
annoying  in  the  reflex  of  many  eyes." 


CHAPTER  III. 

Schematic  Eye  Practice  and  Its  Importance  to  Students. 
— Model  Eyes  and  the  Exercise  of  Care  in  Their 
Adjustment. — Reduction  and  Transposition  of  Lens 
Values,  and  the  Necessity  for  the  Complete  Mas- 
tery OF  This  Work  in  Successful  Skiametry. 

SCHEMATIC  EYE  PRACTICE.  Skill  is  called  "famil- 
iarity with  and  dexterity  in  the  execution  of  any  science,  art  or 
handicraft,"  and  no  division  of  optometry  calls  for  more  prac- 
tice work,  in  order  to  be  skillful,  than  does  skiametry. 

It  is  exceedingly  tiresome  to  a  patient  to  sit  quietly  and 
have  some  inexperienced  student  gaze  for  minutes  through  the 
peep-hole  of  a  mirror  because  he  is  unable  to  correctly  determine 
the  shadow's  action.  But  with  an  experienced  examiner  it  is 
different,  all  he  needs  is  one  or  two  flashes,  or  excursions  of 
the  reflected  light,  and  the  behavior  of  the  shadow,  under  usual 
conditions,  is  made  plain. 

Skill  in  this  work  can  only  come  through  experience,  and 
experience  gained  through  the  use  of  a  metal  or  paste-board 
model  eye  is  just  as  valuable  to  the  student  as  though  it  was 
gained  through  looking  into  a  living  organ  of  vision. 

Students  can  begin  with  large  ocular  pupils,  and  then,  as 
their  skill  increases,  these  pupils  can  be  made  smaller  and 
smaller.  The  expert  in  any  field  where  skill  is  a  factor  is  the 
one  who  practises  morning,  noon  and  night,  or  at  every  oppor- 
tunity that  presents  itself. 

Human  eyes,  owing  to  variations  in  the  pigmentation  of 
the  fundus  and  to  the  uneven  thickness  of  the  corneal  tissue 
giving  rise  to  what  is  called  "irregular"  astigmia,  are  factors 


48 


SCHEMATIC   EYE  PRACTICE 


that  make  some  living  eyes  most  difficult  to  measure  by  means 
of  the  shadow  test,  so  if  an  examiner  makes  himself  a  thorough 
master  of  the  model  eye,  where  conditions  can  be  made  ideal, 
he  will  have  far  less  trouble  with  living  eyes  than  if  this  pre- 
liminary practice  on  the  model  eye  has  been  neglected. 

Fig.  i8. 


THE      DE  ZEXG-STANDARD       SCHEMATIC    EYE. 


SCHEMATIC  EYES.  For  research  work,  as  well  as  for 
practise,  a  good  schematic  eye  requires  careful  selection  and 
adjustment.  The  metal  and  pasteboard  models  that  are  on  sale 
in  all  first-class  optical  supply  houses  offer  a  most  excellent 
means  for  beginners  to  familiarize  themselves  with  the  prin- 
ciples of  both  skiametry  and  opthalmoscopy.  These  eyes,  how- 
ever, are  frequently  imperfect  in  construction,  and  the  printed 


SCHEMATIC    EYES 


49 


scales  attached  to  them  are  often  unreHable.  As  a  consequence^ 
the  student  is  apt  to  meet  with  discouraging  resuhs  in  his  initial 
efforts  to  use  them.  Fig.  i8  shows  one  of  the  newer  makes  of 
the  all-metal  kind,  which  has  five  sizes  of  pupil. 

The  backs  of  these  eyes  are  arranged  for  the  insertion  of 
colored  miniature  plates,  which  serve  to  illustrate  the  various 
pathologic  conditions  of  the  retina,  and  are  to  be  used  in  con- 
nection with  the  study  of  ophthalmoscopy  and  the  use  of  the 
ophthalmoscope.  The  double  cell  in  front  of  the  model  eye 
makes  it  of  excellent  service  in  skiametric  practice ;  as  the  well 

Fig.  19. 


QUEEN  S    PASTEBOARD    SCHEMATIC     EYE. 


marked  axis  scale  also  aids  a  beginner  in  obtaining  the  merid- 
ional accuracy  which  is  so  necessary  to  good  work. 

The  cheap  pasteboard  model,  such  as  shown  in  Fig.  19,  is 
usually  found  to  be  almost  as  trustworthy  as  the  more  expen- 
sive ones,  but  all  of  them  require  testing  before  their  findings 
can  be  implicitly  relied  upon. 

A  good  way  to  determine  the  accuracy  of  these  models  for 
skiametric  purposes  is  to  have  an  experienced  skiametrist  put 
them  to  actual  test  by  first  setting  the  scale  at  "o,"  and  then,  if 
a  one-diopter  convex  spherical  lens  causes  a  reversal  of  the 
shadow  in  all  meridians  at  exactly  forty  inches  away,  it  is  quite 


50  SCHEMATIC    EYES 

safe  to  rely  on  other  findings  made  by  means  of  the  same  model. 
To  prove,  however,  that  the  scales  are  properly  spaced  it  is  wise 
to  first  test  a  few  of  the  numbers  on  each  side  of  the  "o"  before 
depending  upon  them  for  accuracy,  for  in  optometric  work  in 
general  it  is  so  easy  to  be  wrong  and  so  difficult  to  be  precisely 
right. 

All  kinds  of  ordinary  errors  of  refraction  can  be  artificially 
created  by  means  of  these  model  eyes  together  with  a  few  trial 
lenses.  For  instance,  if  an  examiner  is  operating  at  a  distance 
of  forty  inches  away,  by  setting  the  model  so  that  it  shows  one 
diopter  of  myopia  and  then  by  adding  a  one-diopter  concave 
cylindric  lens,  he  can  create  an  error  of  one  diopter  of  hyperopic 
astigmia.  A  one-diopter  convex  cylinder  can  be  used  to  produce 
myopic  astigmia  of  equal  amount.  Setting  the  model  to  show 
two  diopters  of  m^yopia  and  then  using  a  one-diopter  convex 
cylinder  lens  will  create  a  compound  error  of  minus  one-diopter 
spheric  combined  with  a  minus  one-diopter  cylindric,  due  allow- 
ance of  one  diopter  having  been  made  for  the  working  distance. 

With  the  model  showing  two  diopters  of  hypermetropia,  if 
a  two-diopter  concave  cylindric  lens  be  added,  the  exact  com- 
pound quantity  represented  by  this  error  would  be  plus  two 
diopters  of  spheric  combined  with  plus  two  diopters  of  cylindric. 
And  to  neutralize  it  skiametrically  at  a  distance  of  forty  inches 
away  would  require  an  added  lens  power  equal  to  plus  three 
diopters  spheric  combined  with  plus  two  diopters  cylindric.  The 
added  diopter  of  plus  spheric  representing  the  false  myopia, 
often  called  the  "working  quantity." 

To  illustrate  a  mixed  astigmatic  condition  the  model  can  be 
set  to  show  two  diopters  of  myopia,  and  then  by  adding  a  minus 
two-diopter  cylinder  at  axis  90  an  error  representing  minus  one- 
diopter  cylinder  axis  180  combined  with  a  plus  one-diopter 
cylinder  axis  90  can  be  obtained,  which  would  require 
the  addition  of  this  lens  quantity,  or  its  equivalent,  to  neutralize 
it  by  means  of  the  one-meter  shadow  test.    And  it  will  be  noted 


REDUCTION   OF    LENSES  5 1 

that  at  whatever  axis  the  cyhndric  lens  is  set  the  axis  of  the 
artificial  astigmia  will  be  in  the  same  meridian.  Thus  it  will 
be  seen  that  a  schematic  eye  can  be  made  a  very  useful  and 
patient  patient. 

REDUCTION  OF  LENSES.  In  practical  examination- 
room  work  with  the  skiascopic  mirror  it  frequently  happens 
that  a  saving  of  time  and  trouble  is  efifected  by  making  a  test 
right  over  the  patient's  own  glasses ;  this  test  resulting,  perhaps, 
in  the  discovery  that  a  compound-lens  quantity  needs  to  be 
either  added  to  or  subtracted  from  the  lenses  then  in  use. 
Upon  neutralizing  these  glasses  it  is  found  that  they,  too,  are 
of  the  so-called  "compound"  type,  therefore  an  examlHer  must 
be  possessed  of  knowledge  that  will  enable  him  to  tell  the  exact 
ray-bending  power  of  the  four  lens  quantities  involved  and  to 
do  it  with  ease  and  without  waste  of  time  or  likelihood  of  mak- 
ing mistakes.  Now  while  this  subject  is  not  classified  as  be- 
longing to  theoretic  skiametry,  yet  it  is,  nevertheless,  a  very  im- 
portant factor  in  contributing  toward  successful  shadow  work, 
and  especially  so  in  connection  with  the  dynamic  method,  for  ski- 
ametry is  sometimes  considered  as  neutralisation  at  long  range. 
Therefore  a  few  pages  will  here  be  given  to  what  is  thought 
to  be  a  very  simple  solution  of  a  so-called  complex  subject. 

In  the  consideration  of  most  problems  there  is  the  unit  or 
lowest  appreciable  quantity  to  be  dealt  with,  so  it  is  with  lenses. 
Speaking  microscopically  the  basis  of  all  lenses  can  be  said  to  be 
prisms,  but  speaking  macroscopically,  the  unit  of  all  lenses  is  a 
cylinder.  Therefore,  if  it  is  learned  how  to  combine  these  cylin- 
ders, after  having  reduced  all  lens  quantities  to  a  cylindric  basis, 
the  transposition  of  lenses  will  be  found  to  be  a  very  easy  task, 
no  matter  whether  the  lens  quantities  dealt  with  number  few  or 
many. 

This  principle  is  much  like  the  one  in  the  old  story  related 
of  the  quack  doctor  who  had  two  bottles  of  medicine  with 


52 


REDUCTION    OF    LENSES 


which  he  could  cure  all  the  ills  that  flesh  was  heir  to.  His  plan 
was  to  give  doses  out  of  one  bottle  which  turned  every  ailment 
into  fits,  then  the  remedy  in  the  other  bottle  cured  the  fits,  and 
the  patient  got  well. 

To  carry  out  a  similar  procedure  it  must  be  considered  that 
two  cylindric  lenses  of  like  kind  and  strength  when  crossing  one 
another  at  right  angles  are  equal  to  a  spheric  lens.  Hence  the 
reverse  follows,  that  a  spheric  lens  is  equal  to  two  cylindric 
lenses  crossing  one  another  at  right  angles,  and  whose  kind  and 
strength  are  the  same. 

In  the  optometrist's  consideration  of  cylinders  he  will  never 
need  them  at  any  other  than  at  right  angles  to  one  another,  no 


Fig.  20. 


^/n^ 


-h^D 


TWO    CYLINDRIC    LENSES    OF    UNEQUAL    FOCUS    AND    AXIS. 


matter  whether  they  are  plus  and  plus  or  minus  and  minus,  of 
the  same  or  unequal  strengths,  or  whether  they  are 
plus  and  mi}ius  or  minus  and  plus,  equal  or  unequal,  etc.,  etc. 
Their  axes  will  always  be  at  right  angles,  and  for  the  simple 
reason  that  if  they  were  crossed  at  any  other  than  right  angles 
their  combined  refraction  would  show  a  sphero-cylindric  effect, 
which  could  be  duplicated  by  right-angle  cylinders. 

Now,  in  a  combination  of  cylindric  lenses  of  unequal 
strength,  but  of  the  same  kind,  it  will  be  seen  that  when  their 
axes  are  at  right  angles  to  each  other  their  combined  refraction 
will  be  equal  to  that  of  a  compound  lens  whose  component  parts 


REDUCTION   OF   LENSES 


53 


are  of  a  like  nature :  as  a  plus  one-diopter  cylinder  set  at  right 
angles  to  a  plus  two-diopter  cylinder  is  equal  to  a  plus  one- 
diopter  spheric  combined  with  a  plus  one-diopter  cylindric.  The 
second  cylinder  in  the  above  case  having  been  robbed  of  a 
quantity  equal  to  the  strength  of  the  first  cylinder,  in  order  to,. 


■/■^I}' 


A  CROSSED-CYLINDER  LENS  OF  UNEQUAL  MERIDIONAL  FOCUS: 

convert  the  first  one  into  a  spheric  quantity.     The  robbery  is 
noted  and  due  allowance  made  therefor. 

By  referring  to  Fig.  20  it  will  be  seen  that  the  cylinder  lens 
"a"  has  a  ray  bending  power  of  plus  i.  D.,  while  cylinder  lens 


Fig.  22. 


//-^ 


//Z7 


THREE    CYLINDRIC    LENSES    OF    EQUAL    FOCUS.       ONE   AT    AXIS    9O 
AND  TWO  AT  AXIS    180. 


//i^ 


"b"'  has  a  power  of  plus  2.  D.  Their  axes,  of  course,  are  at 
right  angles  to  each  other,  also  to  their  ray  bending  power.  If 
these  two  lenses  were  merged  back  to  back  their  appearance 
would  be  illustrated  by  Fig.  21. 


54 


REDUCTION   OF    LENSES 


Instead  of  two  cylinders  being  used,  one  plus  i.  D.  and  the 
other  plus  2.  D.,  it  is  shown  in  Fig.  22  that  three  plus  i.  D.  cylin- 
ders can  be  employed  to  accomplish  the  same  purpose  as  those 
in  Fig.  20. 

In  Fig.  23  it  is  shown  that  lens  "a"  has  been  converted 
into  a  I.  D.  spheric  quantity  by  the  use  of  the  borrowed  lens 
"c"  of  Fig.  22,  and  as  it  takes  "c"  and  "d"  to  equal  the  plus 
2.  D,  of  "b"  in  Fig.  20  it  is  plain  that  "d"  is  the  remaining 
quantity.     Thus  the  formula: 

+  I.  D.  C.  axis  90  3  +  2.  D.  C.  axis  180  equals  -f-  i-  D-  S. 
C  +  I-  D.  C.  axis  180, 


Fig.  22,. 


-f-lD 


ONE   CROSSED-CVLINDER  OF   EQUAL   MERIDIONAL   FOCUS   AND  ONE 
SIMPLE    CYLINDER    AT    AXIS    iSo. 


Except  for  purposes  of  analysis,  the  crossed  cylinder  is 
never  to  be  generally  employed,  he  who  prescribes  it  other- 
wise only  exhibits  his  ignorance  of  lenses  and  their  uses,  as 
the  function  of  a  lens  is  to  bend  rays  of  light,  and  it  matters 
little  whether  this  bending  is  done  by  two  cylinders  crossing 
one  another  at  right  angles  or  whether  it  is  accomplished  by 
means  of  a  lens  where  one  surface  has  a  spheric  curvature. 
This  rule  also  applies  to  "toric"  lenses  where  the  curves  of  one 
surface  of  revolution  are  ellipsoidal  in  character,  made  so  by 
having  one  meridian  of  curvature  either  greater  or  less  than 
the  one  at  right  angles  to  it. 


REDUCTION   OF   LENSES  55 

To  crowd  an  examiner's  head  with  arbitrary  rules  is  likely 
to  lead  to  confusion,  so  that  in  the  case  of  transposing  lenses 
it  is  well  to  simplify  the  process  as  much  as  possible.  There- 
fore, in  imitating  the  method  of  the  quack  doctor  with  his  two 
medicines,  it  will  be  necessary  to  first  reduce  all  lens  quantities 
to  a  cylindric  basis  and  then  commit  to  memory  two  short  rules 
for  the  transposition  of  cylinders.  The  following  extra  long 
combination  may,  perhaps,  serve  to  make  this  reduction 
principle  plainer: 

+  I.  D.  S.  C  +  2.  D.  C.  90  C  —  I.  D.  C.  180  C  +  I.  D. 
S.  C  —  2.  D.  C.  90  C  —  2.  D.  S. 

Here,  it  is  seen,  there  are  six  lens  quantities  whose  chief 
axes  are  90  and  180  degrees.  After  creating  two  columns,  all 
of  the  lens  quantities  are  written  in  their  cylindric  equivalents 
whose  axes  come  under  these  two  headings,  not  forgetting  that 
each  spheric  lens  is  to  be  written  twice  as  it  is  equal  to  two 
crossed  cylindric  ones  whose  strength  and  kind  are  the  same. 
The  following  is  then  obtained : 

Axis  go  Axis  180 

+  1.  +1. 

+  2.  —  I. 

+  1.  +1. 

—  2.  —  2. 

—  2.  

—  I. 


o 

In  the  axis  90  column  the  totals  are  -\-  4.  D.  and  —  4.  D., 
which,  of  course,  neutralize  one  another.  In  the  axis  180 
column  the  totals  of  —  3.  D.  and  -|-  2.  D.  leave  a  remainder 
of  —  ,1.  D.  axis  180. 

Take  this  example  for  instance: 

+  0.50  D.  C.  45  C  +  0.25  D.  S.  C  +  0.25  D.  C.  135. 


56  REDUCTION   OF   LENSES 

Here  the  two  chief  axes  are  45  and  135  degrees,  and  pro- 
ceeding as  before  the  results  are : 

Axis  43  Axis  I  S3 

+  0.50  +  0.25 

+  0.25  +  0.25 


+  0.75  +  0.50 

The  totals  give  one  cylinder  of  +  0.75  axis  45  to  be  crossed 
by  another  cylinder  of  +  0.50  D.  axis  135,  the  symbols  being 
alike. 

Now  another  example  in  reduction: 

4-  1.25  D.  S.  C  —  1-75  D-  C.  15  C  —  0.75  D.  S. 
O  —  0.25  D.  C.  105. 

Being  reduced,  the  results  obtained  are : 

Axis    13  Axis  103 

+  1.25  +  1-25 

—  175  —  075 

—  0.75  —  0.25 


—  1-25  +  0.25 

This  gives  a  total  of  one  cylinder  of  —  1.25  D.  axis  15  being 
crossed  by  another  cylinder  of  -J-  0-25  D.  axis  105,  the  symbols 
being  unlike. 

In  the  three  examples  shown  all  lens  quantities  have  been 
converted  into  cylindric  equivalents,  so  that  in  order  to  master 
them  the  two  short  rules  before  mentioned  must  be  used  for 
the  transposition  of  these  cylinders,  and  then  the  simple  les- 
son will  have  been  acquired. 

TRANSPOSITION  OF  LENSES.  Rule  No.  i.—In  a 
combination  of  cylindric  lenses  of  a  like  character,  such  as  plus 


TRANSPOSITION    OF    LENSES 


57 


and  plus,  or  minus  and  minus,  the  strength  of  the  weakest 
cylinder  should  be  written  as  the  spheric  quantity  while  the 
DIFFERENCE  between  the  tivo  lenses  should  be  written  as  a  new 
cylindric  quantity,  the  axis  of  the  stronger  cylinder  governing 
the  axis  of  the  cylinder  in  combination,  thus: 

-j-  0.75  D.  C.  axis  45  C  +  0.50  D.  C.  axis  135  should  be 
written  as  equal  to  -(-  0.50  D.  S.  C  +  0.25  D.  C.  axis  45. 

Rule  No.  2. — In  a  combination  of  cylindric  lenses  of  dif- 
ferent character,  such  as  plus  and  minus,  or  minus  and  plus, 
the  strength  of  either  cylinder  can  be  zvritten  as  a  spheric  quan- 
tity while  the  (arithmetical)  sum  of  the  two  cylinders  should 


^/.£SD. 


CROSSED-CYLINDRIC  LENS  OF  PLUS  AND  MINUS  CURVATURES. 


be  written  as  a  new  cylindric  quantity,  the  axis  of  the  second 
lens  governing  the  axis  of  the  cylinder  in  combination,  thus: 

—  1.25  D.  C.  axis  15  C  +  0-25  D.  C,  axis  105, 

can  be  written  in  two  ways,  the  better  way  being  to  write  it 
with  the  minus  quantity  first,  so  as  to  obtain  a  periscopic  effect 
in  the  completed  lens,  this  produces : 

—  1.25  D.  S.  C  +  1-50  D.  C.  axis  105. 

Or  an  equal  refractive  quantity  can  be  obtained  by  writing 
it  in  this  way: 

+  0.25  D.  S.  C  —  I-50  D.  C.  axis  15, 

Fig.  24  shows  a  plus  0.25  D.  C.  lens  "a"  at  axis  90,  being 


58 


TRANSPOSITION    OF    LENSES 


crossed  at  right  angles  by  a  minus  1.25  D.  C.  lens  "b."  Fig.  25 
shows  that  the  plus  0.25  D.  cylinder  "a"  must  be  crossed  by  a 
plus  0.25  D.  cylinder  "c"  in  order  to  convert  the  "a"  lens  into 
a  spheric  quantity,  and  that  the  "b"  cylinder  must  then  be  in- 
creased to  minus  1.50  D.  in  order  to  produce  a  ray  bending 
power  of  minus  1.25  D.  after  the  strength  of  the  borrowed  lens 
"c"  has  been  neutralized. 


Fig.  25. 


-^ffjsn. 


y-O.SSD 
THREE    CYLINDRIC     LENSES,    TWO   PLUS   AND  ONE   MINUS. 


-^501) 


It  will  be  noted  in  Rule  No.  2  that  the  word  " arith'^etical" 
is  parenthesized,  this  is  done  to  indicate  that  for  purposes  of 
common  understanding  liberties  have  been  taken  with  an 
algebraic  problem. 

To  re-transpose  any  of  these  combinations  it  is  only  neces- 
sary to  proceed  by  the  usual  reduction  to  cylindric  form  and 
then  apply  whichever  one  of  the  two  simple  rules  that  may  be 
called  for. 

There  is  one  other  form  of  transposition  which  it  might  be 
well  to  mention  here,  and  that  is  in  the  changing  of  plus  and 
plus  and  minus  and  minus  compounds  into  plus  and  minus  or 
minus  and  plus  equivalents  for  the  purpose  of  producing 
meniscus  forms  of  lenses.  For  instance,  the  following  two 
formulas  "a"  and  "b"  have  like  ray  bending  powers,  also  "c" 
and  "d." 


TRANSPOSITION    OF    LENSIiS  59 

a.  +  I.  D.  S.  C  +  I-  D.  C.  axis     90,  or 

b.  +  2.  D.  S.  C  —  I-  D-  C.  axis  180 

and 

c.  —  I.  D.  S.  3  —  I-  D.  C.  axis  180,  or 

d.  —  2.  D.  S.  C  +  I.  D.  C.  axis     90. 

The  rule  governing  this  transposition  is  as  follows: 

Rule  No.  3. — Add  the  two  lens  quantities  together  for  a 
new  sphere,  change  the  symbol  of  the  cylinder  and  alter  its 
axis  ninety  degrees. 

The  world,  metaphorically  speaking,  takes  off  its  hat  to 
the  mathematician,  so  if  the  optometrist  desires  that  deference 
be  shown  him,  too,  he  must  acquire  enough  of  mathematics  to 
make  himself  proficient  in  his  work. 

Procrastination  and  the  plea  of  "no  time  to  take  up  higher 
optics"  will  neither  advance  the  individual  nor  the  profession 
to  which  he  belongs.  Self-education  is  just  as  good  as  any 
other  kind,  provided  it  accomplishes  its  object;  therefore  let 
him  who  desires  to  make  substantial  skiametric  advancement 
remember  that  the  greatest  service  he  can  do  himself  is  to 
thoroughly  master  the  rudiments  of  light  and  lenses  and  to 
acquire  the  ability  to  juggle  with  all  kinds  and  quantities  of 
ray  and  lens  values. 


CHAPTER  IV. 

Why  Ocular  Pupils  Appear  Red  When  Viewed  Through 
A  Skiascope  With  a  Brief  Description  of  the  Card- 
inal Points  Involved  in  Static  Skiametry,  as  Prac- 
tised WITH  the  Plane  Mirror,  Including  Some 
Theories  Regaiuding  Fundus  Reflex. 

WHY  PUPILS  APPEAR  RED.  Before  considering 
retinal  illumination  it  will  be  well  to  again  call  attention  to 
the  fact  that  all  visible  objects  that  do  not  generate  light  must, 
of  course,  reflect  it,  hence  every  non-luminous  object  that  can 
be  seen  may  be  considered  as  being  some  kind  of  a  mirror. 
Glass  with  amalgam  backing,  as  before  stated,  makes  the  best 
reflector,  while  a  dark  uneven  surface,  like  black  velvet,  makes 
the  poorest.  With  a  so-called  "looking  glass"  the  rays  of  light 
are  reflected  in  an  almost  unbroken  manner,  whereas  with  most 
visible  objects  their  surfaces  are  such  as  to  break  up  the  light 
into  irregular  rays,  or  angles  of  reflection.  This  breaking  up 
being  well  illustrated  by  a  lamp  having  a  clear  glass  chimney, 
and  one  whose  chimney  is  of  the  ground  or  "frosted"  kind.  In 
the  clear  glass  the  flame  is  the  true  source  of  light.  In  the 
ground  glass  the  surface  of  the  chimney  is  the  apparent  source. 

The  inner  back  part  or,  so-called^  fundus  of  an  eye  is  about 
the  same  sort  of  a  mirror  as  rough  red  tissue  paper  makes,  and 
as  it  is  necessary  to  illuminate  this  fundus  in  order  to  obtain  an 
apparent  source  of  light,  or  target,  from  which  to  measure 
emergent  rays,  it  will  be  seen  that  consideration  of  why  the 
pupil  of  an  eye  appears  red  through  the  peep-hole  of  a  skia- 
scope will  be  well  for  all  students  to  understand,  reference  is 
therefore  to  be  had  to  Figs.  26,  2y  and  28. 


WHY  PUPILS  APPEAR  RED 


6i 


In  Fig.  26  the  candle  "a"  radiates  light  rays  which  fall  on 
card  "b"  and  pass  through  the  aperture  "c"  thus  illuminating  a 
portion  of  card  "d." 

Fig.  26. 


d  L-^    b  a 

ILLUMINATION   OF  SECOND  CARD  THROUGH   HOLE  IN   FIRST  ONE. 


Card  "d"  being  something  of  a  mirror,  reflects  the  light  from 
the  illuminated  spot,  or  area,  "e"  in  all  directions,  some  of 
which,  of  course,  passes  back  again  through  the  aperture  "c" 
in  card  "b,"  as  shown  in  Fig.  27.    An  eye,  therefore,  at  "f"  in 

Fig.  27. 


RETURN  RAYS  FROM  SECOND  CARD  ENTERING  EYE  THROUGH  TUBE 

IN   CANDLE. 


order  to  see  the  edge,  or  any  portion,  of  the  illuminated  area 
"e"  on  card  "d,"  must  be  placed  behind  a  tube  "h,"  which  passes 
through  the  flame  of  the  candle  "a,"  where  it  will  then  be  en- 
abled to  intercept  the  returning  rays  from  "e." 


62 


WHY  PUPILS  APPEAR  RED 


In  Fig.  28,  the  skiascope  "g,"  having  a  peep-hole  in  the 
center  of  its  mirror,  practically  replaces  the  tube  "h,"  shown  in 
candle  "a,"  of  Fig.  27.  The  eye  "f"  in  Fig.  28  is  therefore 
enabled  to  see  the  illuminated  area  "e"  on  card  "d."  Now,  by 
enclosing  cards  "b"  and  "d"  in  the  rim  of  a  hollow  sphere  and 
placing  a  lens  over  the  aperture  "c"  in  card  "b,"  there  would  be 

Fig.  28. 


SUBSTITUTING  A  SKIASCOPE  FOR  CANDLE  TUBE. 


created  the  optical  principles  of  a  real  eye  whose  pupil  would 
appear  red,  because  the  fundus  of  the  eye  would  be  visible  to 
an  observer.  This  observer  could  then  readily  see  the  posterior 
inner  surface  of  the  eye  where  the  mesh  work  of  blood  vessels 
gives  it  the  usual  pink-like  appearance  so  familiar  to  the  expe- 
rienced examiner.  It  follows,  therefore,  that  the  reason  why 
the  pupil  of  an  eye  ordinarily  appears  black  is  because  returning 
rays  can  not  be  intercepted  without  using  an  instrument. 


RETINAL    ILLUMINATION  63 

RETINAL  ILLUMINATION.  Subjective  optometry  can 
be  said  to  be  the  treating,  or  bending,  of  rays  of  light  before 
they  enter  an  eye,  whereas,  objective  optometry  can  be  called  the 
bending  of  the  rays  after  they  leave  the  eye. 

Rays  entering  an  eye  can  be  of  two  kinds,  those  that  proceed 
direct  from  some  light  source,  such  as  a  lamp  flame,  and  those 
that  are  reflected  from  some  kind  of  a  mirror.  In  either  case 
the  fundus  of  the  eye  is  illuminated,  and  the  intensity  of  the 
illumination  is  dependent  upon  the  distance  that  the  rays  have 
traveled,  and  to  the  quality  of  the  mirror  that  reflects  them. 

Rays  traveling  in  the  form  of  a  beam  of  light  can  be  made 
to  enter  the  eye  parallel,  convergent  or  divergent,  and  the  size 
of  the  retinal  illumination  is  dependent  upon  this  parallelism, 
convergency  or  divergency. 

Retinal  illumination  is  a  necessity  in  skiametry,  because 
some  kind  of  a  target,  or  apparent  light  source,  must  be  ob- 
tained from  which  the  emergent  rays  can  emanate,  and  the 
means  for  obtaining  this  target  is  to  be  had  by  reflecting  light 
from  a  lamp  flame  into  a  patient's  eye,  and  then  by  intercepting 
the  returning  or  reflected  rays,  at  the  peep-hole  of  a  skiascope, 
an  examiner  is  in  a  position  to  measure  these  rays  and  thus  to 
determine  the  state  of  the  patient's  refraction. 

Two  factors  in  skiametric  work  must  be  kept  in  mind,  namely, 
that  the  entering  rays  are  solely  for  the  purpose  of  creating  a 
source  from  which  the  emerging  rays  can  start,  while  it  is  the 
angle  of  the  emerging  rays,  alone,  which  denotes  the  refractive 
condition  of  the  eye,  and  it  is  the  measurement  of  these  emergent 
rays  that  gives  the  name  of  shadow  measuring  to  skiametry. 
The  so-called  "shadow"  being  created  by  the  inner  edge  of  the 
iris,  which  limits  the  size  of  the  illuminated  area  on  the  retina, 
made  by  the  entering  rays  of  light. 

Errors  of  refraction,  and  the  distance  from  the  external 
light  source,  serve  to  influence  the  sise  of  the  retinal  light  spot, 
and  this,  in  turn,  influences  the  speed  and  brightness  of  the 


64 


RETINAL  ILLUMINATION 


shadow  in  its  skiascopic  behavior,  butj^t  has  no  direct  bearing 
upon  the  refraction  of  the  eye  under  measurement,  as  the 
emergent  rays  originate  from  the  internal  light  source  created 
by  the  illumination  on  the  retina,  and  it  is  the  movement  of  the 
edge  of  this  light  spot  that  gives  the  with  and  against  motions 
of  the  shadow,  made  mention  of  later  on. 

In  Fig.  29,  "a."  is  the  external  light  source,  "b"  is  the  skia- 
scope, "c"  the  lens  system  of  the  eye,  "d"  the  retinal  illumina- 
tion, or  light  spot,  and  "f"  the  focus  of  the  entering  rays,  which 
the  retina  stops  at  "d." 

Fig.  29. 


ILLUMINATING   THE   OCULAR   FUNDUS. 


The  size  of  "d,"  it  will  be  easily  seen,  is  regulated  by  the 
positions  of  "a"  and  "b,"  for  if  the  light  source,  or  the  mirror, 
is  near  to  the  eye  then  "d"  will  be  larger  than  if  either  one  were 
farther  away. 

Fig.  30  shows  the  fundus  of  an  eye  with  an  illuminated  area 
of  light,  "e,"  the  shadow  being  represented  by  "d,  d,  d,  d,"  while 
"g"  calls  attention  to  the  demarcation  between  "d,  d,  d,  d,"  and 


SHADOW    PHENOMENA 


65 


"e."  This  demarcation  creating  the  edge  of  a  target,  or  curved 
line  of  light,  acting  as  a  source  from  which  measurements  can 
be  calculated. 

Fig.  30. 


THE  ILLUMINATED  AREA  ON  THE  FUNDUS. 

SHADOW  PHENOMENA.  In  Fig.  31  the  marginal  line 
"g,"  between  the  light  spot  "e"  and  the  non-illuminated  area 
"d"  "d"  constitutes  the  starting  point  for  the  emerging  rays,  and 

Fig.  31. 


RAYS    RETURNING    FROM    EDGE    OF    ILLUMINATED    AREA    ON    THE 

FUNDUS. 


if  the  lens  system  "c"  is  in  proper  relation  to  the  target  "g," 
producing  what  is  known  as  emmetropia,  the  rays  will  emerge 
parallel. 


66  SHADOW    PHENOMENA 

On  the  other  hand,  if  the  emerging  rays  diverge  or  converge 
in  one  or  more  meridians  of  the  eye  it  denotes  an  error  of  re- 
fraction of  some  kind. 

When  a  convex  lens  of  known  power  is  placed  in  front  of  an 
emmetropic  eye,  as  shown  by  "k"  in  Fig.  32,  the  emerging 
parallel  rays  will  be  brought  to  a  focus,  or  crossing  point,  at  the 
focal  length  of  the  lens  used,  and  if  at  this  focal  point  an  exam- 
iner places  his  own  eye  behind  the  peep-hole  of  a  skiascope,  at 
"h,"  he  will  be  unable  to  note  any  motion  of  "g,"  or  of  any 
appearance  of  a  shadow  in  the  pupil  of  the  patient's  eye.  On 
the  contrary,  if  he  advances  toward  the  patient  so  that  the 
point  of  crossing  of  the  emergent  rays  is  behind  his  own  eye,. 


Fig.  32. 


g       \  J/  k  h 

RETURNING  RAYS  INFLUENCED  BY  A  CONVEX  LENS. 

then  he  can  note,  if  he  is  skillful,  that  "g"  now  appears  as  the 
edge  of  a  pupillary  shadow  and  moves  with  the  movement  of 
the  light  on  the  patient's  face  as  he  rotates  his  skiascopic  mirror 
from  side  to  side  or  top  to  bottom  across  the  eye.  And  if  the 
eye  is  emmetropic  this  movement  of  the  shadow  will  be  alike  in 
all  meridians  of  rotation. 

The  reverse  order  prevails  if  the  examiner  recedes  from  his 
patient,  so  that  the  focus,  or  crossing  point  of  the  emergent  rays, 
is  in  front  of  his  own  eye,  then  all  rotations  of  his  skiascopic 
mirror  cause  the  shadow  to  move  against  the  light  that  is  re- 
tlectcd  on  the  patient's  face.  This  crossing  point  of  the 
emergent  rays  then  becomes  known  as  the  "point  of  reversal" 
of  the  shadow,  and  this  reversal  point  enables  an  examiner  to 


THE  shadow's  action  6/ 

determine  the  refractive  status  of  his  patient's  eye,  either  by 
altering  the  distance  of  his  view-point,  or  by  changing  the 
strength  of  lens  "k"  so  the  rays  v^ill  focus,  or  cross,  at  any 
given  point  selected.  The  difference  between  the  lens  an  eye 
ougJit  to  take  to  produce  the  shadow's  action  at  a  given  point, 
and  the  lens  it  actually  does  talze,  constitutes  the  measurement 
of  the  error. 

THE  SHADOW'S  ACTION.  Just  why  the  shadow  be- 
haves in  the  with  and  against  manner  here  described  can  be- 
seen  by  reference  to  Figs.  33  and  34. 

In  Fig.  33,  if  a  single  ray  is  followed  from  the  point  of  the 

Fig.  33. 


PaT/enfj    eye,  Cxamineris     eye 

WHY   THE   SHADOW    MOVES    ''wITh"    THE    MIRROR. 

arrow,  "e,"  on  the  fundus  of  the  patient's  eye,  to  "e"'  on  the 
fundus  of  the  examiner's  eye,  the  two  arrows  will  be  seen  to 
point  in  the  same  downward  direction.  All  motion  can  then 
be  said  to  be  syncJironous,  or  coincident,  as  the  upper  emergent 
ray  from  the  patient's  eye  becomes  the  upper  entering  ray  of 
the  examiner's  eye. 

In  Fig.  34,  owing  to  the  refraction  by  lens  "k,"  the  upper 
emergent  ray  from  the  arrow's  point  "e"  in  the  patient's  eye  be- 
comes the  lozver  entering  ray  of  the  examiner's  eye,  and  the 
arrow  "e"  undergoes  a  reversal  of  position  at  "e"'  by  pointing 
upward.  Motion  can  then  be  said  to  be  opposite,  or  against  the 
skiascopic  movement  of  the  facial  light. 


68 


THE  SHADOW  S  ACTION 


It  is  this  motion  of  the  shadow  zvith  and  against  the  skia- 
scope's  movement  that  enables  an  examiner  to  locate  the  cross- 
ing "x"  of  the  emergent  rays,  and  the  distance  from  the  patient's 
eye  at  which  this  crossing  occurs,  together  with  the  lenses  neces- 
sary to  cause  it,  constitute  the  means  for  determining  the  meas- 
urement of  the  error.  Thus  if  a  plus  1.50  D.  lens,  "k,"  is 
required  to  create  a  crossing  of  the  rays  at  forty  inches  from  an 
emmetropic  eye,  whose  accommodation  is  relaxed,  then  the 
error  would  be  plus  0.50  D.,  because  plus  i.  D.  is  the  correct 
strength  for  a  lens  necessary  to  cause  a  crossing  at  this  distance. 

If  a  lens  of  only  plus  0.25  D.  caused  a  crossing  of  the  rays  at 
forty  inches  from  the  patient's  eye,  then  the  error  would  be 


Fig.  34. 


Patlenfi  eye  *  f'xaminci'^    eye 

WHY  THE  SHADOW  MOVES  '"aGAINST"  THE  MIRROR. 


minus  0.75  D.  And  if  twenty  inches  was  the  distance  selected 
for  the  crossing,  then  plus  2.  D.  would  be  the  working  lens  "k," 
from  which  calculations  should  be  made,  instead  of  plus  i.  D. 
Skiametry  has  been  ably  described  by  Burnett  as  being  con- 
trolled by  the  law  of  conjugate  foci,  therefore  if  an  emmetropic 
or  hyperopic  eye  is  made  artificially  myopic,  the  strength  of  the 
lens  required  to  produce  this  artificial  myopia  must  enter  into 
the  final  calculations.  And  if,  on  the  other  hand,  the  eye  has 
true  myopia,  then  the  amount  of  the  error  can  be  easily  deter- 
mined by  finding  the  crossing  point  of  the  emerging  rays.  Thus 
if  the  rays  crossed  at  fifty-three  inches  from  the  patient's  eye 
the  error  would  be  neutralized  by  a  lens  of  minus  0.75  D      If 


THE  shadow's  imitation  69 

the  crossing  was  at  twenty-two  inches  distance,  then  the  lenses 
needed  would  be  minus  1.75  D. 

THE  SHADOW'S  IMITATION.  Fig.  35  will  convey  a 
slight  idea  of  the  appearance  of  a  so-called  "shadow"  in  passing 
across  the  pupil  of  an  eye. 

A  much  better  illustration  of  this  shadow  phenomenon  can  be 
had  by  taking  a  piece  of  cardboard,  say  six  inches  square,  and 
cutting  a  hole  in  it  one  inch  in  diameter,  then  by  pasting  over 
this  aperture  a  piece  of  pink,  translucent  paper,  and  by  holding 
the  card  before  a  lamp,  a  fair  idea  of  the  reddish  appearance  of 
the  pupil  of  an  eye  when  looked  at  through  a  skiascope  may  be 

Fig.  35. 


PUPILLARY  APPEARANCE  OF  A  SO-CALLED     SHADOW. 

had.  The  edge  of  another  piece  of  cardboard  passed  between 
the  first  card  and  the  lamp  will,  by  varying  the  distance,  give  a 
very  good  representation  of  the  shadow  as  seen  in  an  eye  by 
means  of  a  skiascope. 

SHADOW  MEASURING.  All  eyes  must  be  measured  in 
two  or  more  meridians,  so  as  to  determine  the  greatest  and 
least  refraction.  If  these  two  are  vertical  and  horizontal,  and  a 
plus  I.  D.  S.  is  placed  before  a  patient's  eye  and  the  shadow  is 
found  to  reverse  at  forty  inches  in  the  horizontal  meridian,  and 
at  twenty  inches  in  the  vertical,  then  the  error  could  be  neu- 
tralized by  a  lens  of  minus  i.  D.  C.  axis  180,  but  if  it  took 
plus  I.  D.  in  the  vertical  and  plus  2.  D.  in  the  horizontal,  then 


yo  SHADOW    MEASURING 

the  lens  required  would  be  plus  i.  D.  C.  axis  90.  Or  if  it  took 
plus  2.  D.  in  the  vertical  and  plus  3.  D.  in  the  horizontal,  then 
plus  I.  D.  S.  combined  with  plus  i,  D.  C.  90  would  be  the  lens 
indicated. 

It  will  be  noted  that  i.  D.  of  artificial  myopia  was  first 
created  for  the  forty  inches  observation  point,  then  in  the  final 
deductions  this  created  myopia  was  allowed  for. 

If  true  myopia  was  present  then  no  artificial  myopia  would 
be  needed,  unless  the  true  was  weaker,  and  had  a  point  of 
crossing  farther  away  than  the  point  of  observation.  To  illus- 
trate this,  suppose  the  true  myopia  was  a  half-diopter,  the 
emergent  rays  would  then  cross  at  eighty  inches,  and  if  forty 
inches  was  selected  as  the  point  of  observation  the  crossing  of 
the  rays  would  occur  back  of  the  examiner's  skiascope,  and  the 
motion  of  the  shadow  would  be  zvith  the  mirror,  the  same  as  in 
emmetropia  without  lenses.  In  emmetropia,  however,  the  plac- 
ing of  a  plus  I,  D.  lens  ^before  the  patient's  eye  would  cause 
crossing  at  forty  inches,  but  in  a  true  myopia  of  a  half-diopter  the 
plus  I.  D,  lens  serves  to  overdo  the  matter,  therefore,  a  plus 
0.50  D.  would  be  the  needed  lens,  or,  if  the  observation  was 
changed  to  twenty-six  inches  then  the  crossing  could  be  found 
without  changing  the  i.  D.  lens.  So  the  rule,  before  mentioned, 
that  the  difference  between  that  which  an  eye  does  take  and 
that  which  it  ouglit  to  take,  to  cause  reversal  at  a  given  point, 
represents  the  error  of  refraction  in  the  meridian  measured. 

PRACTICE  OF  STATIC  SKIAMETRY.  In  the  practical 
application  of  static  skiametry,  a  fifty-candle  power  light  source 
should  be  situated  at  the  patient's  right,  on  a  level  with,  and 
from  six  to  twelve  inches  from,  his  ear.  After  placing  a  trial 
frame  before  the  patient's  eyes,  two  plus  4.  D.  S.  lenses  are 
to  be  inserted  in  each  cell  of  the  frame  and  the  patient  directed 
to  look  over  the  examiner's  shoulder  at  some  object  placed 
twenty  or  more  feet  away,  the  examiner  to  be  seated  squarely 


PRACTICE    OF    STATIC    SKIAMETRY  7I 

in  front  of  the  patient  and  operating  his  piano  skiascope  exactly 
forty  inches  from  the  patient's  eyes.  In  emmetropia,  under  these 
conditions,  the  shadow  will  move  against  the  mirror  in  all 
meridians,  and  the  four  diopters  of  lens  power  will  have  to  be 
reduced  to  one  diopter  before  reversal,  or  the  neutralizing  point 
of  the  emerging  rays,  occurs,  the  plus  one-diopter  lens  being 
the  so-called  "working  quantity"  for  an  examination  that  is 
made  at  forty  inches. 

In  hypermetropia  of,  say,  one  diopter  the  reduction  of  the 
four-diopter  lens  would  be  two  diopters.  And  of  these  two 
diopters  one  diopter  would  represent  the  error,  and  the  other  the 
working  quantity  or  artificial  myopia  necessary  to  create  a 
standard  condition,  variations  from  which  are  to  be  measured 
by  adding  or  subtracting  lenses,  or  by  altering  the  distances  at 
which  observations  are  made.  This  can  be  illustrated  as  fol- 
lows :  In  a  true  myopia  of,  say,  two  diopters  the  movement  of 
the  shadow  would  still  be  against  the  mirror,  even  after  the  four- 
diopter  lens  had  been  removed,  the  examiner  could  then  add 
minus  spheric  lenses,  or  he  could  advance  his  skiascope  up  to 
within  twenty  inches  of  the  patient's  eyes,  as  the  emergent  rays 
from  the  retina  of  an  eye  having  two  diopters  of  true  myopia 
would  have  a  conjugate  focus  at  this  distance. 

Had  the  eye  been  myopic  one  diopter,  the  conjugate  focus 
would  have  been  exactly  at  forty  inches  without  lenses  of 
any  kind,  hence  the  rule  in  calculating  all  errors  of 
refraction  in  static  skiametry,  where  the  working,  or  observation, 
distance  is  forty  inches,  is  to  add  one  diopter  of  minus  quantity 
to  the  total  findings,  and  this  sum  will  then  represent  the  error. 
Astigmia  being  truly  a  half-spherical  error  the  examiner  is  to 
proceed  as  in  simple  hypermetropia  or  myopia,  with  the  excep- 
tion that  the  error  is  to  be  measured  only  in  the  meridian  at 
right  angles  to  the  axis,  and  the  axis  is  to  be  determined  by 
noting  the  meridian  in  which  there  is  no  motion  of  the  shadow 
when  the  zvorking  lens  is  in  position. 


'J2  PRACTICE    OF    STATIC    SKIAMETRY 

Take  as  an  example  a  patient  with  two  diopters  of  hyperopic 
astigmia  in  the  horizontal  meridian ;  if  the  examiner  operates  at 
forty  inches  with  a  plus  one-diopter  spherical  lens  before  the 
patient's  eye  he  will  note  a  marked  movement  with  the  mirror  in 
the  horizontal  meridian,  but  no  movement  in  the  vertical,  this 
being  the  meridian  of  no  error  it  is  of  course  the  axis.  So,  after 
noting  this  axis,  by  the  general  band-like  appearance  of  the 
shadow,  and  that  the  error  at  right  angles  to  this  axis  is 
hyperopic,  all  that  remains  for  the  examiner  to  do  is  to  de- 
termine how  great  the  error  really  is,  and  this  is  ascertained 
by  adding  plus  lenses  until  reversal  occurs. 

Lenses  used  for  neutralizing  purposes  can  be  either  spheric 
or  cylindric,  for  it  will  be  remembered  that  two  cylinders  of 
equal  strength  and  kind  with  their  axes  crossing  one  another  at 
right  angles  are  equal  to  a  sphere.  Therefore  any  astigmia  where 
the  axis  is  vertical  can  be  measured  by  the  aid  of  a  spheric  lens 
used  in  its  horizontal  meridian,  the  vertical  meridian  being  ig- 
nored. Where  cylindric  lenses  are  used  great  care  must  be  exer- 
cised in  placing  the  axis  of  the  cylinder  so  it  exactly  coincides 
with  the  astigmatic  axis  of  the  eye,  otherwise  confuson  of 
shadow-action  and  inaccuracies  will  occur. 

So-called  "compound"  and  "mixed"  errors  can  be  considered 
as  being  astigmatic  in  the  two  meridians  of  greatest  and  least 
refraction  that  are  at  right  angles  to  each  other.  After  a 
working  lens  is  in  position,  suppose  it  takes  a  plus  one-diopter  to 
arrest  the  motion  in  the  vertical  meridian,  and  a  plus  two-diopter 
to  do  the  same  in  the  horizontal,  then  the  case  could  be  likened 
to  a  one-diopter  cylinder  being  crossed  by  a  two-diopter  cylin- 
der, which,  if  transposed,  would  resolve  itself  into  the  following 
formula:  plus  i.  D.  S.  combined  with  a  plus  i.  D.  C.  axis  90. 

Looking  at  it  another  way,  if  the  vertical  meridian  had  taken 
a  minus  instead  of  a  plus  lens  to  neutralize  its  error  the  formula 
would  then  read  minus  i.  D.  C.  axis  180  crossed  by  a  plus 
2.  D.  C.  axis  90,  or  transposed  it  would  equal  a  minus  i.  D.  S. 


THEORIES  REGARDING  DULL  REFLEXES  'J'^ 

combined  with  a  plus  3.  D.  C.  axis  90,  so  that  all  cases  of  com- 
pound and  mixed  errors  are  merely  cases  of  crossed  cylinders, 
and  are  capable  of  neutralization  by  either  spheric  or  cylindric 
lenses. 

THEORIES  REGARDING  DULL  REFLEXES.  In 
the  consideration  of  a  subject  as  broad  as  the  term  ocular 
skiametry  would  indicate,  the  temptation  of  an  author  to  soar 
his  kite  in  the  realm  of  speculation  and  attach  to  its  tail  a  few 
theories  of  his  own  is  very  great  indeed,  even  if  some  of  the 
theories  should  prove  "bad  pennies"  and  return  to  embarrass 
their  giver. 

In  the  actual  practice  of  skiametry  there  arise  certain  little 
details  which  might  be  considered  as  sub-phenomena,  and  which 
exercise  a  more  or  less  important  bearing  upon  the  system  as  a 
whole.  Attention  will  therefore  be  invited  to  a  few  of  these 
points  which  may  perhaps  savor  more  of  theory  than  they  do  of 
practice  but  which,  nevertheless,  seem  to  answer  natural  ques- 
tions likely  to  arise  in  the  mind  of  those  who  desire  to  know  the 
why  of  everything  they  are  interested  in. 

Ocular  pupils  of  a  size  not  exceeding  two  millimeters  in 
diameter,  notwithstanding  an  examiner's  ability  to  magnify 
them,  are  often  very  troublesome  and  constitute  a  part  of  the 
cases  which  it  is  wise  to  determine  by  means  other  than  by 
skiametry.  This  is  especially  true  if,  in  addition  to  the  small- 
ness  of  the  pupil,  the  fundus  reflex  is  of  the  deeply  pigmented 
or  dull  kind.  The  reason  for  this  is  due  not  so  much  to  a  failure 
on  the  part  of  the  examiner  to  see  the  pupil  as  it  is  to  the  fact 
that  the  pupillary  aperture  prevents  a  sufficient  volume  of  light 
from  entering  the  eye  in  order  to  create  a  shadow  sharp  enough 
in  outline  to  be  readily  measured. 

In  expecting  to  occasionally  find  some  dull  ocular  fundi 
the  examiner  must  not  mistake  high  degrees  of  myopia,  nor 
hyperopia,  for  excessive  pigmentation.     Especially  in  myopia, 


74 


THEORIES  REGARDING  DULL  REFLEXES 


even  in  an  error  of  only  four  or  six  diopters,  will  the  examiner 
sometimes  be  puzzled  to  determine  why  the  reflex  is  so  poor. 
Adding  correcting  glasses,  however,  often  brightens  this  reflex 
in  proportion  as  the  correction  nears  the  total,  although  at 
the  exact  reversal  point  of  the  shadow  the  reflex  may  again 
become  very  unsatisfactory,  as  may  also  the  movements  of  the 
shadow  at  this  time. 

A  slow  motion  must  not  be  mistaken  for  no  motion.     For 

Fig.  36. 


WHY    THE    RETINAL    ILLUMINATION    IS    LARGER    IN    AMETROPIA 
THAN   IN  EMMETROPIA. 


if  Fig.  36  is  looked  at  it  will  be  seen  why  pronounced  degrees 
of  either  myopia  or  hyperopia  make  large  light  areas  on  the 
retina,  thus  requiring  a  longer  time  for  the  shadow  surround- 
ing the  light  circles  "b"  and  "c"  to  come  into  view  than  if 
these  illuminated  areas  were  smaller. 

Fig.  37  also  shows  this  principle  emphasized  in  a  myopic 
eye,  the  returning  rays  from  the  edge  "d"  of  the  illuminated  area 
"b"  illustrating  the  distance  the  shadow  must  traverse  before 
reaching  the  opposite  side,  this  area  being  much  larger  than 


THEORIES  REGARDING  DULL  REFLEXES  75 

if  the  eye  was  an  emmetropic  one,  where  the  proportion  would 
be  similar  to  "a"  in  Fig.  36. 

The  fact  that  a  reflex  in  a  given  error  of  myopia  is  much 
duller  than  in  a  corresponding  one  of  hypermetropia  is  due, 
no  doubt,  to  the  greater  distance  the  returning  rays  travel  in 
a  myopic  eye  than  in  an  emmetropic  or  hyperopic  one  before 
reaching  the  pupillary  opening  which,  consequently,  diminishes 

Fig.  37. 


WHY    SHADOWS    MOVE     SLOWER    IN     AMETROPIA    THAN     IN 
EMMETROPIA. 

their  number  through  radiation  and  absorption.  Fig.  38  illus- 
trates a  theory  for  this.  The  lines  "h'  e'  m'"  show  the  relative 
loss  by  quenching  as  the  divergent  rays  from  a  given  illumina- 
tion on  the  retina  of  a  myopic,  emmetropic,  or  hyperopic  eye 
strike  the  inside  of  the  iris,  which  serves  to  diaphragm  part  of 
them  and  prevent  their  further  egress.  The  hyperopic  eye, 
owing  to  its  shorter  depth,  permits  of  the  least  interference 
with  its  radiation,  but  its  retinal  illumination,  see  "c"  in  Fig. 
36,  shows  why  its  reflex  is  dull,  though  not  as  dull  as  that  of 
the  myopic  eye  "b,"  of  Fig.  36. 

Fig.  39  shows  the  comparative  loss  in  intensity  of  illumina- 


7^ 


THEORIES  REGARDING  DULL  REFLEXES 


tion  in  eyes  whose  myopic  or  hyperopic  error  varies  from  one 
to  sixteen  diopters,  "a"  to  "f"  showing  the  relative  size  of  the 
retinal  area,  illuminated,  and  thus  accounting  for  the  especially 
poor  reflex  in  marked  degrees  of  myopia. 

Brightness  of  reflex,  however,  is  not  all  there  is  to  skiam- 
etry,  for,  owing  to  the  optical  phenomena  called  "penumbra," 
it  is  sometimes  possible  to  obtain  a  more  defined  shadow  under 

Fig.  38. 


WHY  A  SHADOW  IS  DULLER  IN  MYOPIA  THAN  IN  A  LIKE  DEGREE 
OF    HYPERMETROPIA. 


a  moderate  illumination  than  it  is  under  one  more  intense.  A 
reason  for  this  is  suggested  in  Fig.  40.  But  just  what  part 
the  numerous  pennmhrce  play  in  interfering  with  the  sharp- 
ness of  demarcation  of  the  shadow  it  is  difficult  to  ascertain, 
for  the  emerging  light  casts  its  penumbra  at  the  peep-hole 
of  the  examiner's  mirror  just  as  the  entering  light  does  at 
the  pupil.  And  when  it  is  considered  that  a  round  aperture 
is  being  dealt  with  it  will  be  seen  that  the  conditions  are  even 
more  complex  than  would  ordinarily  manifest  themselves  if 
the  shadow  cast  was  a  central  one  instead  of  being  peripheral. 


THEORIES  REGARDING  DULL  REFLEXES 


17 


Figs.  40  and  41  may  serve  to  make  this  subject  better  under- 
stcx)d  for,  as  has  been  said  before,  a  sharp  shadow  is  a  great 
aid  to  good  work. 

Fig.  39. 


RELATIVE   SIZE  OF   RETINAL    ILLUMINATION    IN    HIGH   AND    LOW 
DEGREES    OF    MYOPIA. 


Fig.  40. 


THE  OPTICAL   PRINCIPLES   OF   PENUMBRA. 


In  Fig.  41  the  same  principle  can  be  seen  as  is  shown  in 
Fig.  40,  only  the  conditions  are  doubled,  for  here  there  are 
three  points  on  the  candle  flame  instead  of  two,  the  central 
point  acting  in  a  manner  which  virtually  makes  it  the  same 
as  though  four  points  had  been  selected.     The  opaque  object 


78 


THEORIES  REGARDING  DULL  REFLEXES 


"a"  interferes  with  the  passage  of  the  horizontal  rays  of  light 
from  the  candle  "c."  The  oblique  rays,  however,  pass  at  dif- 
ferent angles  and  give  rise  to  confused  shadows  as  illustrated 
by  "d^"  and  "d^" 

In  Fig.  42  this  principle  has  been  adapted  to  an  eye  where 
two  points  of  illumination  are  again  shown  whose  source  is 
located  on  the  mirror-like  retina,  for  it  is  only  the  center  of 
the  shadow  that  is  involved,  this  shadow  being  produced  by 

Fig.  41. 


THE  OPTICAL   PRINCIPLES  OF   PENUMBRA   DOUBLED. 


the  iris  acting  as  an  opaque  object.  If  either  a  plus  or  minus 
lens  is  placed  in  front  of  this  eye  it  merely  serves  to  refract 
all  the  Hght  in  accordance  with  the  lens  selected,  the  penumbra 
still  remaining  to  add  to  the  indistinctness  of  the  edge  of  the 
shadow. 

If  this  phenomenon  could  be  overcome  it  would,  seemingly, 
contribute  much  toward  that  skiametric  accuracy  for  which  all 
skiametrists  are  striving  but,  as  heretofore  shown,  if  a  gain  be 
made  in  one  direction  a  loss  is  quite  sure  to  follow  in  another, 
so  that  examiners  must  be  content  with  fuzzy  shadows  until 


THEORIES  REGARDING  DULL  REFLEXES 


79 


some  one  solves  the  problem  of  how  to  get  rid  of  them  with>^ 
out  interfering  with  the  valuable  points  already  secured  in 
dealing  with  other  conditions. 

Operating  at  a  distance,  in  order  to  produce  parallelism 
of  the  rays,  seems  at  present  to  be  the  only  means  of  over- 
coming this  phenomenon,  but  this,  of  course,  bars  out  the  use 

Fig.  42. 


INTERFERENCE  OF  PENUMBRA  IN  SHADOW  TESTING. 


of  many  tests  and  methods  which  have  been  found  of  great 
service  in  uncovering  ciliary  spasm  and  latent  errors,  etc.  Thus 
it  will  be  seen  that  many  contributing  factors  toward  both 
success  and  failure  enter  into  the  problem  of  accurately  estimat- 
ing the  refraction  of  an  eye  "independent  of  a  patient's 
intelligence." 


CHAPTER  V. 

Theory  of  Dynamic  Skiametry,  and  the  Importance  of 
Reliable  Fixation  in  Co-ordinate  and  Independent 
Observation,  with  a  Reference  to  Three  Essential 
Myopias,  and  an  Explanation  of  "Ray  Values." 

THEORY  OF  DYNAMIC  SKIAMETRY.  The  optics  of 
dynamic  skiametry  can  be  considered  as  being  the  same  as  the 
optics  of  static  skiametry,  one  being  fixation  within  infinity 
while  the  other  is  fixation  at  infinity. 

The  word  "dynamic"  is  derived  from  the  Greek  word 
dynamis,  and  signifies  forces  not  in  equiUbrium,  or  motion  as 
the  result  of  force,  being  the  opposite  of  "static." 

Dynamic  skiametry  then,  as  might  be  readily  inferred,  is 
an  application  of  Bowman's  discovery  made  under  some  kind 
of  force.  This  force  is  the  muscular  one  which  is  familiarly 
known  as  accommodation. 

While  the  static  method  of  practising  skiametry  is  one 
where  the  ciliary  muscle  of  an  eye  is  at  rest,  the  dynamic 
method  is  the  exact  reverse  of  this,  and  is  made  Avhile  the 
accommodation  is  exerting  itself  sufficiently  to  readily  accept 
refractive  assistance  up  to  a  point  where  its  relation  with  an- 
other muscular  force  called  "convergence"  is  interfered  with. 

The  principle  involved  is  a  simple  one.  It  is  well  known 
that  a  pound  weight  placed  upon  the  shoulder  of  a  sturdy 
man  creates  no  appreciable  burden  or  discomfort.  But  load 
this  same  man  down  to  almost  the  limit  of  his  endurance  and 
then  add  this  pound  of  additional  weight  and  its  presence  will  be 
noticed  at  once.  So  it  is  in  dynamic  skiametry,  a  call  is  made 
for  a  pronounced   increase  in  tension  of  the  accommodation 


THEORY   OF   DYNAMIC    SKIAMETRY  8l 

by  having  the  patient  read  a  series  of  test  letters  placed  either 
on  an  examiner's  brow,  attached  to  his  skiascope,  or  to  a  fixa- 
tion stand,  then,  by  varying  this  tension  as  judgment  teaches 
and  by  being  able  to  easily  supply  required  artificial  lens  power, 
the  accommodation  is  reduced  to  its  normal  relationship  with 
convergence.  And  most  eyes,  no  matter  what  the  age  of  the 
patient  may  be,  will  only  surrender  the  accommodative 
excess  which  has  been  required  to  maintain  near-vision.  This 
excess  will  therefore  be  composed  of  what  has  formerly  been 
called  by  the  name  of  "spasm,"  or  "latent"  hypermetropia. 

The  relationship  between  accommodation  and  convergence,  ■ 
if  roughly  stated,  is  found  to  be  in  about  the  proportion  of  one 
to  three  for  the  two  eyes ;  that  is*  when  the  accommodation  is 
exerted  to  the  extent  of  one  diopter,  the  convergence  required, 
according  to  Hartridge,  is  a  little  over  one  and  one-half  de- 
grees for  each  eye.  This,  of  course,  is  subject  to  variation, 
for  when  the  accommodation  equals  ten  diopters  the  conver- 
gence is  estimated  to  be  slightly  over  eighteen  degrees  for 
each   eye. 

Another  way  of  viewing  this  is  to  consider  that  for  every 
diopter  of  accommodation  exerted  there  is  a  corresponding 
meter  angle  of  convergence  called  for,  and  a  meter  angle  is 
described  as  the  angle  created  by  an  imaginary  line  drawn  from 
an  eye  to  a  point  forty  inches  away,  where  it  crosses  another 
line  called  the  "median,"  which  is  drawn  from  midway  be- 
tween the  two  eyes.  Two  meter  angles  converging  at  twenty 
inches  away  would  then  be  in  harmony  with  two  diopters  of 
accommodation,  and  so  on.  To  prove  that  the  relationship 
between  the  two  factors  governing  ocular  adjustment  is  reliable, 
and  that  eyes  under  normal  conditions  do  not  converge  without 
accommodating,  nor  accommodate  without  converging,  the  fol- 
lowing simple  experiment  can  be  made:  Take  a  person  under 
forty  years  of  age  with  known  emmetropia  and  place  him  so 
that  his  eyes  are  exactly  forty  inches  away  from  the  smallest 


82  THEORY    OF   DYNAMIC    SKIAMETRY 

test  type  which  he  can  see  to  read  at  this  distance,  then  while 
he  is  engaged  in  the  act  of  reading  add  a  half-diopter  convex 
lens  quantity  to  both  eyes,  and  it  will  be  noted  that  the  print 
will  be  perceptibly  blurred  or  dimmed.  In  making  this  experi- 
ment be  absolutely  sure  that  there  is  no  latent  error  present,  or 
the  test  will  prove  unreliable. 

Now  this  seems  to  show  that  the  relationship  between  these 
two  forces  is  a  quantity  adjusted  finely  enough  to  be  relied 
upon,  for  without  the  control  of  the  convergence  the  accom- 
modation would  have  immediately  relaxed  when  the  lens  was 
added  which  took  away  the  necessity  for  the  amount  of  mus- 
cular exertion  represented  by  the  fraction  of  one  diopter  which 
the  lens  called  for. 

An  understanding  of  this  point  is  very  essential,  as  it  repre- 
sents the  basic  principle  upon  which  the  dynamic  method  is 
founded.  It  is  well  known  that  both  accommodation  and  con- 
vergence are  elastic  quantities,  as  an  emmetrope  with  normal 
accommodation  can  wear  minus  lenses  up  to  the  limit  of  his 
amplitude  without  producing  diplopia,  also  that  the  adduction 
and  abduction  of  orthophoric  eyes  run  into  large  figures  before 
the  doubling  of  an  object  occurs.  Hence  it  will  be  seen  that 
the  relationship  between  these  two  forces  is  hable  to  vary  in 
accordance  with  the  training  received  by  the  muscles  controlling 
them.  And  these,  in  turn,  by  the  innervation  of  the  nerves  that 
transmit  the  vitalizing  impulses. 

Two  elastic  bands  linked  together,  in  which  the  strength  of 
one  may  be  double  that  of  the  other,  will  find  a  point  of  balance, 
or  equality  of  resistance,  if  stretched  to  any  degree  whatsoever, 
therefore  when  it  is  borne  in  mind  that  accommodation  and 
convergence  always  have  an  individual  balance  for  every  visual 
point  for  which  they  co-operate  it  can  be  understood  why 
axed  rules  for  adapting  prisms  must  prove  unreliable. 

A  case  in  point  may  emphasize  this :  A  person  born  with 
two  diopters  of  hypermetropia  is  compelled  to   suppress   six 


THEORY    OF   DYNAMIC    SKIAMETRY  83 

degrees  of  convergence  while  looking  at  a  distance,  this  becomes 
a  sort  of  habit  which,  owing  to  the  greater  development  of  the 
ciliary  muscles  through  more  than  ordinary  use,  requires  a 
new  standard  of  relationship  to  be  maintained  that  is  adapted  to 
this  special  condition. 

It  might  be  reasoned  that  there  are  two  ways  of  correcting 
such  a  case  as  this,  one  by  relieving  the  tension  on  the  intrinsic 
muscles  with  lenses,  and  the  other  by  adapting  prisms  for  the 
aid  of  the  extrinsic  ones.  In  some  cases  perhaps  both  forms 
of  relief  are  indicated,  but  in  most  cases  the  wise  procedure  is 
to  correct  the  refractive  defect  and  then,  by  time  and  develop- 
ment, train  the  weakened  extrinsic  muscles  up  to  an  approx- 
imate standard  of  "i  to  3"  relationship  with  the  intrinsic  ones. 

Most  eyes  have  some  kind  of  a  refractive  error,  or  else  they 
are  so  placed  in  the  head  that  their  relative  position  as  to 
pupillary  distance  is  at  fault,  and  for  this  reason  there  is  a  sort 
of  individual  equation  in  almost  every  case  which  calls  for 
special  judgment.  And  it  is  this  individuality  that  causes  one 
patient  to  fix  upon  sixteen  inches  as  a  comfortable  reading 
point,  while  another  person,  of  the  same  age,  will  select  a 
twelve-inch  point. 

It  has  been  stated  that  accommodation  is  captain  of  the 
visual  ship,  but  captains  have  other  persons  to  boss  them,  the 
same  as  fleas  are  said  to  have  "other  fleas  to  bite  them,"  etc. 
So  convergence  might  be  called  first  mate,  as  its  influence  is 
undoubtedly  felt  in  the  compromise  that  must  occur  for  all 
binocular  visual  fixation  points.  If  this  was  not  the  case  then 
emmeiropes  would  read  with  comfort  with  spheric  lenses 
of  plus  three  diopters  at  thirteen  inches,  no  matter 
how  young  or  old  the  person  was.  The  facts  are,  however, 
that  an  cmmetrope  with  abundant  amplitude  of  accommodation 
resents  even  a  quarter  of  a  diopter  of  artificial  lens  aid  when 
reading  at  any  near  point,  and  the  reason  therefor  is  because 
the  natural  locking  point,  if  it  can  be  called   such,  between 


84  THEORY   OF   DYNAMIC    SKIAMETRY 

accommodation  and  convergence  has  been  interfered  with.  This 
natural  locking  point,  or  relationship,  constitutes  the  foundation 
upon  which  dynamic  skiametry  rests,  and  it  can  be.  relied  upon 
to  automatically  adjust  itself  to  the  proper  refractive  quantity 
for  any  given  distance — habit,  general  health  and  muscle  inner- 
vation considered. 

In  the  optical  principles  of  static  skiametry,  as  given  in  the 
previous  chapter,  it  was  required  that  the  rays  of  light  ema- 
nating from  the  retina  of  a  patient's  eye  have  a  conjugate  focus 
or,   in  other  words,   that  true  or  false  myopia  be  present  in 

Fig.  43. 


Myofiic    AD 

Skiascope 

TRUE    MYOPIA    (STATIC    METHOD). 

order  to  measure  it,  and  thus  to  secure  data  upon  which  other 
calculations  can  be  based.  Fig.  43  shows  an  eye  with  true 
myopia  of  one  diopter,  hence  emerging  rays  of  light  come  to  a 
natural  focus  forty  inches   away. 

False  myopia  can  be  of  two  kinds,  artificial  and  accommo-^ 
dative.  Artificial  myopia  is  produced  by  using  a  plus  spheric 
trial  lens,  and  accommodative  myopia  is  temporarily  acquired 
by  having  the  patient  look  at  a  fixation  object. 

By  the  static  method  it  is  required  that  a  one-diopter  trial 
lens  be  employed  when  the  working  distance  is  forty  inches 
away,    so   that  artificial   myopia   may   be     produced    and    the 


THEORY    OF    DYNAMIC    SKIAMETRY  85 

emerging  rays  from  an  eye  made  to  focus,  or  cross  one 
another,  at  the  focal  length  of  the  lens  used.  This  is  correct 
for  this  method,  but  for  the  dynamic  method  no  trial  lens  is 
required  to  produce  this  false  myopia^  as  the  crystalline  lens 
of  the  eye  under  examination  takes  its  place.  Fig,  44  will 
perhaps  make  this  plainer,  for  in  the  drawing  the  false  myopia 
under  the  static  method  is  created  by  means  of  a  trial  lens,  the 
eye  being  emmetropic  and  the  rays  emerging  parallel  before 
being  refracted  by  the  plus  i.  D.  trial  lens. 

Fig.  44.  i 


<5hias'cop& 
ARTIFICIAL   MYOPIA    (STATIC  METHOD). 

Under  the  dynamic  method,  Fig.  45,  the  false  myopia 
is  created  by  means  of  an  increase  in  the  convexity  of  the 
crystalline  lens,  better  known  by  the  term  accommodation, 
or  "punctum  accommo datum,"  as  Burnett  calls  it,  the  vision 
being  fixed  on  some  nearby  object. 

This  eye,  the  same  as  in  Fig.  44,  is  emmetropic,  thus  making 
the  two  working  conditions  practically  equal. 

By  the  static  method,  if  the  test  is  to  be  made  at  ten  inches,  a 
four-diopter  convex  lens  must  be  used.  By  the  dynamic 
method  this  four-diopter  convex  lens  power  can  virtually  be 
added  to  the  crystalline  lens  of  the  eye  under  examination  by 
advancing  the  fixation  card  of  the  examiner  up  to  a  distance 


86  THEORY   OF   DYNAMIC    SKIAMETRY 

of  ten  inches  from  the  eyes  of  the  patient,  thereby  causing  the 
accommodation  to  be  exerted  to  this  degree  in  order  that  the 
letters  on  the  card  may  be  distinctly  read ;  this  effort,  or  the 
result  of  it,  is  why  it  is  termed  accommodative  myopia,  as  dis- 
tinguished from  the  lenticular  or  artificial  kind  produced  by  the 
trial  lens. 

To  illustrate  the  value  of  this  method,  and  also  to  show 
its  practical  adaptation,  a  case  will  be  considered  whose  error 
of  refraction  is  two  diopters  of  hypermetropia,  one  diopter  of 
which  is  manifest,  and  one  diopter  latent,  or   in  a  condition 

Fig.  45. 


/Accommodation  /  D. 

<3kia3cofte. 

ACCOMMODATIVE  MYOPIA    (DYNAMIC  METHOD). 

somewhat  spasmodic.  In  examining  this  eye  at  a  distance  of 
forty  inches,  the  patient  looking  at  some  object  twenty  or  more 
feet  away,  it  is  found  that  the  static  method  shows  one  diopter 
of  hyperopia,  as  it  takes  a  two-diopter  convex  lens  to  produce  a 
reversal  of  the  shadow  at  this  distance,  one  diopter  of  which 
represents  the  artificial  myopia,  or  the  working  refraction  re- 
quired. The  dynamic  method  being  used  in  this  case,  it  is  dis- 
covered that  when  the  patient  looks  at  the  fixation  card,  forty 
inches  away,  a  convex  lens  of  a  diopter  and  a  half  can  be  added 
before  a  reversal  of  the  shadow  is  obtained,  the  examiner  then 
advances  so  as  to  make  the  test  at  a  distance  of  thirteen  inches 
and  finds  that  two  diopters  can  be  added  before  reversal  takes 


THEORY    OF   DYNAMIC    SKIAMETRY  8/ 

place.  Advancing  to  within  ten  inches  of  the  patient's  eyes 
makes  no  change.  Withdrawing  to  forty  inches  again,  it  is 
found  that  very  Httle  aheration  in  appearance  of  the  shadow 
has  occurred  unless  the  patient  has  looked  away  in  the  mean- 
time, when  the  spasm  will  most  likely  reassert  itself. 

Now  what  has  taken  place?  The  accommodation  called 
for  by  the  dynamic  method  at  forty  inches  was  one  diopter. 
The  patient  having  two  diopters  of  hypermetropia  had,  there- 
fore, to  make  a  total  accommodative  effort  of  three  diopters, 
in  order  to  see  the  letters  on  the  fixation  card.  The  examiner 
supplies  refractive  assistance  until  one  diopter  and  a  half  of 
convex  lens  quantity  has  been  added,  the  accommodation  relax- 
ing to  this  degree  and  the  shadow  showing  a  reverse  movement. 
Perhaps  this  case  is  one  where  the  age  of  the  patient  is  less 
than  twenty  years,  general  health  considered  good,  and  muscle 
tension,  or  unconscious  habit  of  exertion,  is  suspected  of  being 
vigorous.  A  new  test  is  made  at  a  distance  of  thirteen  inches 
where  the  total  accommodation  called  for  is  five  diopters,  of 
which  two  represent  the  hyperopia  and  three  the  amount  called 
for  in  emmetropia  at  this  distance.  Under  this  burden  the  eye 
will  be  found  to  accept  a  two-diopter  convex  lens  quantity  be- 
fore reversal  occurs.  Repeating  the  test  again  at  ten  inches  no 
more  relaxation  is  found,  thereby  proving  the  second  finding 
to  be  correct. 

To  analyze  still  further,  it  may  be  stated  that  at  thirteen 
inches,  where  an  emmetrope  uses  three  diopters  of  accommo- 
dation, nine  degrees  of  convergence  are  called  for.  A  patient, 
therefore,  who  is  making  five  diopters  of  accommodative  effort, 
ought,  correspondingly,  to  make  fifteen  degrees  of  convergence, 
thus  calling  for  a  distance  of  eight  inches. 

So,  as  before  stated,  while  both  accommodation  and  con- 
vergence seem  somewhat  elastic  they,  nevertheless,  appear  to 
have  a  tendency  to  attain  a  standard  co-ordination  when  dis- 
turbing factors  are  removed. 


88  THEORY   OF   DYNAMIC    SKIAMETRY 

Fig.  46  is  intended  to  illustrate  the  mechanical  action  of 
a  spasm  of  accommodation  equal  to  a  half-diopter.  The  line 
"a"  shows  the  position  of  the  lens  when  the  accommodation 
is  at  rest.  The  line  "b"  shows  its  position  when  the  accommoda- 
tion is  equal  to  a  half-diopter  of  involuntary  effort,  called 
"spasm,"  and  the  dotted  line  "c"  shows  when  the  accommodation 
is  equal  to  one  diopter. 

Fig.  46. 


HOW  THE  ACCOMMODATION   CAN  ABSORB  A   CILIARY   SPASM. 


If  the  Spasm,  or  unconscious  muscle  effort,  equals  a  half- 
diopter,  and  the  patient  be  required  to  look  at  an  object  which 
calls  for  one  diopter  of  accommodation,  then  the  conscious  effort 
will,  of  course,  be  equal  to  the  difference,  or  one  half-diopter 
more.  It  can  thus  be  seen  that  a  spasm  may  be  gotten  rid  of 
by  what  might  be  fittingly  termed  absorption. 

In  applying  this  method  to  cases  where  the  spasm  is  likely 
to  be  greater  than  one  diopter,  such  as  in  children,  or  in  those 
cases  when  heterophoria  is  present,  the  test  should  be 
made  at  a  shorter  distance  than  forty  inches.  Twenty  inches, 
for  instance,  calling  for  two  diopters  of  accommodation,  ten 
inches  for  four  diopters,  and  so  on. 


THEORY   OF   DYNAMIC    SKIAMETRY  89 

Another  view  for  the  elimination  of  spasm  by  the  dynamic 
method  can  be  taken :  A  man  is  told  that  be  owes  one  dol- 
lar which  he  is  desired  to  pay.  He  consults  his  books  and  finds 
that  he  has  already  paid  fifty  cents  of  this  amount.  Then  all 
that  can  be  righteously  collected  of  him  is  the  difference,  or  the 
remaining  fifty  cents.  Now  this  same  man  consults  an  optome- 
trist, and  is  required  to  exert  his  accommodation  equal  to 
one  diopter,  but  having  a  spasm  of  a  half-diopter — and  ocular 
spasms,  as  it  is  known,  are  really  unconscious  muscular  efforts 
• — he  has,  therefore,  unknowingly  contributed  a  half-diopter  of 
accommodation  which  constitutes  one-half  of  the  amount  re- 
quested of  him,  so  he  thus  needs  to  consciously  add  a  half- 
diopter  more  and  the  request  is  fully  complied  with.  If  his 
obligation,  or  error,  had  been  higher  the  request  would  have 
had  to  be  greater,  but  the  principle  is  the  same,  and  so  when  it 
comes  to  actual  tests  made  by  this  method  it  will  be  found  that 
the  theories  here  expounded  will  be  borne  out  in  practice. 

Spasms  of  accommodation  are  now  generally  classified 
under  two  heads — the  toniCj  or  persistent  muscle  effort,  which 
is  often  called  latent  hypermctropia,  and  the  clonic,  or  inter- 
mittent action  of  the  ciliary,  which  is  frequently  met  with  in  ^O 
the  objective  estimation  of  both  hypermetropia  and  myopia,  f 
particularly  the  latter.  Both  kinds,  however,  are  factors  in 
ocular  skiametry  of  which  cognizance  must  be  taken  and 
methods  used  whereby  their  disturbing'  influence  can  be 
overcome. 

It  is  a  rule  that  in  persons  over  forty  years  of  age,  ski- 
ametric  findings  made  by  the  static  method  are  fairly  reliable, 
but  the  drawback  to  the  universal  use  of  this  one  method  lies 
in  the  inability  of  an  examiner  to  differentiate  his  cases  and  to 
tell  in  advance  whether  he  is  dealing  with  a  case  wherein  spasm 
of  accommodation  is  a  factor  until  after  he  has  used  the  dynamic 
method  and  compared  results.  Therefore,  to  save  time  and 
avoid  error,  it  is  wise  for  an  operator  to  use  the  dynamic  method 


90 


RELIABLE    FIXATION 


in^ll  cases  under  fifty  years  of  age;  and  where  the  patient  is 
under  thirty  it  is  best  to  use  this  method  at  as  close  a  point  as 
from  ten  to  thirteen  inches  away. 

RELIABLE  FIXATION.  This  subject,  which  has  a 
direct  bearing  upon  the  question  of  brightness  of  the  fundus 
reflex  and  corresponding  definition  of  the  pupillary  shadow, 
relates  to  the  visual  angle  under  which  examinations  should 
be  made,  also  to  the  point  at  which  the  patient's  accommodation 
is  to  be  adjusted  during  the  observations.  The  point  of  reversal 
of  a  shadow  is  a  very  difficult  one  to  decide  upon  with  any  great 
degree  of  exactness,  for  the  reason  that  at  the  precise  crossing 
point  of  the  returning  rays  the  shadow  is  most  erratic  and  very 
difficult  of  determination  as  to  its  action.  And  as  no  lens 
power  can  be  added  to  or  subtracted  from  a  patient's  accommo- 
dation without  interference  with  this  action,  it  will  readily  be 
seen  that  the  examiner's  mirror  must  be  operated  either  inside 
or  outside  of  a  patient's  exact  point  of  fixation  if  the  behavior 
of  the  shadow  is  to  be  accentuated. 

In  other  words,  if  a  patient  is  looking  at  a  point  exactly 
fifty-three  inches  away,  and  an  examiner  makes  his  observa- 
tion from  a  point  forty  inches  distant,  the  shadow  will  show  a 
hyperopic  movement  equal  to  a  quarter  of  a  diopter.  On  the 
other  hand,  if  the  examiner  views  this  same  eye  from  this 
same  distance  of  forty  inches,  the  patient,  however,  being  re- 
quired to  look  at  a  card  situated  thirty-two  inches  away,  the 
shadow's  action  will  be  a  myopic  one  of  a  quarter  of  a  diopter. 
Fig.  47  will  perhaps  make  this  plainer,  for  here  it  will  be  seen 
that  the  adjustment  of  the  patient's  accommodation  was  first 
made  for  a  distance  equal  to  three-quarters  of  a  diopter,  and 
then  for  a  distance  equal  to  a  diopter  and  a  quarter,  the  observer 
being  at  a  distance  of  one  diopter  in  both  cases,  the  action  of 
the  shadow  was,  therefore,  first  with  the  mirror  and  then  against 
it,  whereas  if  a  test  had  been  made  at  one  diopter  the  shadow. 


RELIABLE    FIXATION  9 1 

of  course,  would  not  have  shown  any  motion.  Thus  it  will  be 
seen  that  the  method  is  not  unlike  solving  the  question  of  the 
exact  middle  of  a  piece  of  string  by  simply  doubling  it,  for  this 
is  what  it  practically  amounts  to. 

In  estimating  the  behavior  of  the  shadow  the  advantage 
gained  by  an  examiner  in  making  his  estimate  from  two  or 
three  focal  adjustments  of  his  patient's  accommodation  is,  of 
course,  just  double  or  treble  that  of  making  it  from  a  single 
point.  Besides,  it  frequently  occurs  that  an  examiner  desires 
to  approximately  ascertain  the  amount  of  any  myopia  present 
before  he  changes  his  lenses.     All  he  has  to  do,  then,  is  to 

Fig.  47. 


MULTIPLE    FIXATION    AND    OBSERVATION    POINTS. 

advance  his  mirror  nearer  to  his  patient  while  the  latter  is  still 
looking  at  the  forty-inch  fixation  point.  If  he  finds  that  the 
shadow  does  not  reverse  until  the  mirror  is  advanced  to  within 
twenty  inches  of  the  eye  under  examination,  then  he  knows 
that  the  myopia  present  is  about  two  diopters,  one  of  which 
represents  the  error  and  the  other  the  accommodation.  And  if 
he  has  to  advance  up  to  within  ten  inches  before  obtaining  a 
reversal  he  then  knows  that  the  error  is  nearer  to  three  diopters, 
and  so  on. 

The  means  for  accomplishing  these  results  are  very  simple 
indeed.  Fig.  48  shows  a  fixation  stand,  ana  the  manner  of  its 
construction  which,  as  can  be  seen,  is  merely  a  light-weight 
nickel-plated  brass  stand  carrying  a  card  having  dots  upon  it 


92 


INITIAL    EXAMINATIONS 


which  the  patient  is  asked  to  count.  The  stand  being  movable, 
and  adjustable  as  to  height,  permits  of  its  usefulness  in 
many  ways. 

Fig.  49  shows  the  style  of  card  this  stand  can  carry,  on 
the  reverse  side  of  which  is  printed  a  small  astigmatic  dial,  Fig. 

Fig.  48. 


AUTHORS  FIXATION   STAND. 

50,  which  is  merely  a  convenience  to  be  used  in  other  tests  not 
concerned  with  skiametry.  This  stand,  however,  can  be  made 
to  do  excellent  duty  as  a  dynamic  astigmometer,  enabling  sub- 
jective measurements  to  be  taken  at  any  near  point  desired. 

INITIAL  EXAMINATIONS.  In  initial  skiametric  tests 
the  card.  Fig.  49,  is  usually  placed  about  a  foot  behind  an  ex- 
aminer's head,  several  inches  to  his  right,  and  high  enough  for 


INITIAL   EXAMINATIONS 


93 


its  dots  to  be  illuminated  by  the  light  source  used,  Fig.  51, 
showing  the  relative  position  of  light,  examiner,  patient  and 
fixation  card. 

In  operation  the  examiner  requests  his  patient  to  first  look 
at  the  dots  on  the  fixation  card,  fifty-three  inches  away.     In 

Ftg.  4Q. 


Count  the  Dots. 

FIXATION-STAND  TARGET  CARD. 


Fig.  50. 
10  80  90  100  u^ 


REVERSE  SIDE  OF  FIXATION  CARD. 

making  his  lens  changes  he  stops  with  the  shadow  moving 
slightly  with  the  mirror,  then  he  requests  the  patient  to  look 
at  fixation  target  cards  on  his  skiascope.  If  he  gets  a  reversal 
of  the  shadow  he  knows  that  he  is  very  close  to  a  correction  for 
this  distance.    He  then  proceeds  to  finish  the  test  and  eliminate 


94 


INITIAL    EXAMINATIONS 


the  presence  of  any  ciliary  spasm  by  moving  the  mirror  and  its 
targets  nearer  to  the  patient,  and  at  the  same  time  crowding  on 
all  the  convex  lens  quantity  possible  without  producing  an 
against  motion. 

The  card  on  the  fixation  stand  may  be  used  in  place  of  the 
skiascope  card  for  the  shorter  focal  tests,  but  it  will  not  be  found 
as  convenient.  The  greatest  advantage  to  be  derived  from  the 
employment  of  the  fixation  stand,  however,  lies  in  the  angle  at 
which  an  eye  can  be  viewed,  also  in  the  apparent  brilliancy  and 
enlargement  of  the  patient's  pupil,  which  is  due,  no  doubt,  to  a 

Fig.  51. 


POSITION   FOR  INITIAL  EXAMINATION. 


corresponding  decrease  in  light  stimulation.  But,  be  that  as  it 
may,  the  use  of  the  fixation  stand  in  most  cases  is  productive  of 
much  better  initiaj  results  than  accrue  when  its  use  is  dispensed 
with.  Especially  is  this  true  where  the  examiner  is  somewhat 
lacking  in  the  experience  which  comes  only  with  years  of 
practice. 

The  system  of  multiple  cards,  or  fixation  points,  has  an 
added  value  to  an  examiner  from  the  fact  that  it  enables  him  to 
make  the  first  observation  of  a  patient's  eye  under  the  most 
favorable  conditions  possible  for  obtaining  a  bright  fundus 
reflex.  He  can  then  govern  himself  accordingly  in  further 
examination  of  the  case. 


RAY    VALUES  95 

If  the  reiiex  is  a  bright  one,  the  change  of  vision  from 
stand  to  skiascope  card  will  not  materially  affect  its  brilliancy. 
On  the  other  hand,  if  the  reflex  is  poor  then  further  tests 
should  be  continued  by  aid  of  the  stand,  which,  being  light 
in  weight,  its  position  can  be  easily  altered  by  the  examiner. 

There  is  another  very  valuable  feature  connected  with  the 
use  of  independent  -fixation  points,  and  that  is  in  the  estimation 
of  weak  errors  of  refraction  by  instructing  a  patient  to  look 
back  and  forth  from  skiascope  to  fixation  stand  while  the  dis- 
tance of  these  two  from  the  patient's  eye  differs  slightly. 

RAY  VALUES.  The  term  "ray"  is  used  in  preference  to 
the  term  "wave,"  simply  for  purposes  of  easy  explanation  and 
ready  comprehension;  therefore,  from  the  foregoing,  it  will  be 
understood  how  important  it  is  for  an  examiner  to  have 
a  thorough  knowledge  of  ray  values  as  well  as  of  lens  values. 
And  by  "ray  values"  is  meant  the  strength  of  the  lens  that 
would  be  required  to  parallel  a  ray  of  light  when  intercepted 
at  any  distance  from  its  source.  Fig.  2  in  the  first  chapter 
emphasizes  this  principle.  The  value  of  a  ray  ten  inches  from 
its  source  is  4.  D. ;  at  thirteen  inches,  3.  D. ;  at  sixteen  inches, 
2.50  D. ;  at  twenty  inches,  2.  D. ;  at  twenty-six  inches,  1.50  D. ; 
at  forty  inches,  i.  D.,  and  so  on. 

In  using  both  static  and  dynamic  skiametry  the  position 
of  an  examiner  and  the  dioptric  values  of  his  lenses  in  their 
relation  to  his  patient's  visual  fixation  are  all  factors  in  the 
correct  estimation  of  ocular  errors.  Thus,  if  a  patient  is  look- 
ing at  an  object  situated  eighty  inches  distant,  and  a  skiametric 
examination  is  made  at  forty  inches  away,  the  ray  value  at 
eighty  inches  may  be  said  to  equal  a  half-diopter,  while  its  value 
at  forty  inches  is  one  diopter ;  one  less  a  half  leaves  a  half,  and 
the  shadow  under  these  conditions  will  behave  as  though  the 
error  were  a  half-diopter  of  hypermetropia. 

If  the  patient  was  looking  at  an  object  forty  inches  away, 


96  RAY   VALUES 

and  the  examiner  viewed  the  eye  through  the  skiascope  at  a 
distance  of  eighty  inches,  then  the  reverse  would  of  course 
be  the  case,  and  the  error  indicated  would  be  a  half-diopter 
of  myopia. 

All  of  this,  however,  presupposes  that  the  examiner  knows 
just  what  his  patient's  accommodation  is  doing,  and  so  by 
having  fixation  cards  situated  at  forty,  fifty-three,  eighty,  one 
hundred  and  sixty,  and  three  hundred  and  twenty  inches  away, 
respectively,  it  would  be  possible  for  an  examiner  working 
at  one  meter  to  observe  the  shadow's  action  in  the  four  quar- 
ters of  a  diopter  of  hypermetropia.  This  would  necessitate  the 
securing  of  an  especially  intelligent  and  obedient  patient,  to- 
gether with  expert  skill  on  the  part  of  an  examiner. 

Later  on  it  will  be  seen  that  other  methods  can  be  used, 
where  the  intelligence  of  the  patient  is  not  so  important  a  factor. 
The  same  principle  governing  ray  values,  however,  can  be 
applied  to  shorter  distances.  Thus,  a  patient  with  a  one-diopter 
convex  trial  lens  before  his  eye,  when  looking  at  a  fixation 
card  forty  inches  away,  can  be  measured  for  a  quarter,  a  half, 
or  three-quarters  of  a  diopter  of  hypermetropia,  if  the  exam- 
iner will  carefully  measure  the  distances  from  his  patient's 
eye  so  as  to  hold  his  mirror  exactly  thirty-two  inches  away 
when  he  is  measuring  for  three-quarters  of  a  diopter,  twenty- 
six  inches  away  when  he  is  measuring  for  a  half,  twenty-two 
inches  away  when  he  is  measuring  for  a  quarter,  and  so  on, 
the  ray  value  modifying  the  lens  value  and  the  two  combined 
influencing  the  total.  In  fact,  in  skiametry  the  determination  of 
ray  values  can  perhaps  be  summed  up  by  deducting  the  value 
of  what  the  ray  is  actually  doing  from  what  it  really  ought  to 
do  under  the  circumstances. 

The  possibilities  in  the  way  of  juggling  with  accomm,oda- 
tion,  lens  values,  ray  values  and  the  shadoiv,  are  almost  limit- 
less, and  it  is  to  be  expected  that  as  ocular  skiametry  and  its 
methods  become  better  known  there  will  be  found  many  more 


RAY    VALUES  97 

ways  of  applying  its  principles  which  may  not  be  all  fully 
understood  at  this  time.  As  the  student  acquaints  himself 
with  the  principles  involved  in  ray  and  lens  values,  however,  he 
will  find  that  the  practical  side  of  his  work  can  be  made  much 
easier.  The  following  examples,  too,  may  show  the  applica- 
tion of  some  of  the  more  important  points :  When  an  eye  looks 
at  an  object  situated  forty  inches  away  it  must  exert  its  accom- 
modation at  least  one  diopter.  Place  a  plus  one-diopter 
spherical  lens  over  this  eye  and  if  it  is  emmetropic  the  emergent 
rays  will  converge  at  a  point  twenty  inches  away.  One  diopter 
will  then  represent  the  accommodation,  and  one  diopter  the  trial 
lens,  or  artificial  myopia,  making  a  total  of  two.  If  a  plus  two- 
diopter  lens  is  used,  the  point  of  convergence  will  be  at  thirteen 
inches;  if  a  plus  three-diopter  is  employed,  it  will  be  at  ten 
inches ;  the  accommodative  myopia  increasing  the  total  myopia. 

Now  suppose  a  patient  has  an  error  of  two  diopters  of 
hypermetropia,  then  what  occurs  when  a  three-diopter  lens 
is  added?  Why,  the  accommodation  under  the  stress  of 
carrying  a  burden  immediately  surrenders  its  error,  read- 
justs its  accommodation  and  convergence  to  a  relationship  of 
least  resistance,  and  there  is  left  only  one  diopter  of  what  we 
call  artificial  myopia,  and  one  of  accommodative  myopia.  The 
point  of  convergence  of  the  emergent  rays  would  then  be  at 
twenty  inches,  instead  of  at  ten  inches,  which  Avould  be  the 
point  of  crossing  of  the  rays  from  an  emmetropic  eye  under 
the  same  conditions  of  lens  and  accommodation.  Therefore  it 
will  be  seen  that  where  the  rays  ought  to  cross  is  at  ten  inches, 
and  where  they  do  cross  is  at  twenty.  The  difference  in  ray 
value  being  two  diopters — the  amount  of  the  error. 

In  cases  of  this  kind  it  is  only  natural  for  a  student  to  ask 
why  an  eye  under  these  conditions  does  not  surrender  more 
than  two  diopters,  especially  when  it  is  exerting  its  accommo- 
dation one  diopter  for  fixation.  In  reply  it  can  be  said  that, 
without  compulsion,  an  eye  which  is  making  three  degrees  of 


98  RAY   VALUES 

convergence  will  naturally  try  to  make  one  diopter  of  accommo- 
dation in  order  to  maintain  the  harmony  of  the  theoretic  stand- 
ard of  one  to  three  relationship.  This  explanation  can  also  be 
given  to  account  for  the  discomfort  an  emmetrope  of,  say, 
twenty  years  of  age,  experiences  when  attempting  to  read  at 
thirteen  inches  distance  with  a  pair  of  half-diopter  plus  spheric 
lenses  on,  his  accommodation  and  convergence  will  not  be  in 
accord.  The  convergence  required  at  thirteen  inches  is  nine 
degrees,  which  calls  for  a  co-ordination  of  three  diopters  of 
accommodation,  but  try  to  reduce  this  accommodation  by  even 
a  quarter-diopter  and  the  harmony  will  be  disturbed,  causing 
discomfort  to  manifest  itself. 

In  true  myopia,  of  one  diopter,  similar  conditions  of  ray 
and  fixation  values  are  present,  one  diopter  for  accommodation 
at  forty  inches,  and  one  for  the  true  myopia,  make  two,  the 
ray  value  of  which  is  twenty  inches.  In  all  pronounced  errors 
of  refraction  an  examiner  must  ever  bear  in  mind  that  the 
relationship  of  one:  to  three  between  accommodation  and 
convergence  may  have  been  upset,  and  a  different  co-ordi- 
nation established.  Measurements  in  myopic  cases  frequently 
vary  under  ray  and  lens  value  procedure,  but  while  skiametry 
always  gives  the  refraction  exactly  as  it  is  under  the  existing 
conditions,  these  conditions  may  be  such  as  to  trouble  an 
examiner  in  the  formation  of  his  judgment.  Hence  measure- 
ments taken  in  different  ways  are  productive  of  better  results. 

In  measuring  cases  by  ray  values  a  student  can  work  out 
any  combination  if  he  is  well  grounded  in  these  principles. 
Simple,  compound  or  mixed  cases  of  astigmia  are  merely  to 
be  solved  by  measurement  of  meridians,  as  for  instance :  An 
eye  having  one  diopter  of  hyperopic  astigmia,  axis  vertical,  in 
fixing  at  forty  inches  with  a  plus  one-diopter  spheric  lens 
before  it  would  show  reversal  of  the  shadow  in  the  horizontal 
meridian  at  forty  inches,  and  at  twenty  in  the  vertical. 


RAY   VALUES  99 

In  a  myopic  eye  represented  by  the  correcting  formula  of 
minus  i.  D.  S.  combined  with  minus  i.  D.  C.  axis  i8o  and 
fixing  at,  say,  twenty  inches,  reversal  would  occur  in  the 
vertical  meridian  at  ten  inches  and  in  the  horizontal  at  thirteen. 
The  student  can  therefore  see  that  the  whole  subject  is  practi- 
cally one  of  figures,  where  axis  and  error  are  always  to  be  con- 
sidered as  at  right  angles  to  one  another,  and  that  myopia  may 
be  classified  as  of  three  kinds  :  true,  accommodative  and  artiUciaL 


CHAPTER  VL 

Orthophoric  and  Heterophoric  Conditions,  and  the  In- 
fluence OF  Habit  Upon  Accommodation  and  Con- 
vergence, With  Special  Consideration  of  Spasms  and 
THE  Use  of  Prisms. 

ORTHOPHORIA  AND  HETEROPHORIA.  In  order 
to  again  emphasize  the  strong  points  of  dynamic  skiametry  it 
will  be  wise  to  further  consider  ocular  muscle  action  and  note 
its  relation  to  other  factors  that  are  involved  in  the  production 
of  binocular  vision,  both  with  and  without  so-called  strain. 

The  perfect  balance  of  the  extrinsic  muscles,  termed  ortlw- 
phoria,  is  a  rare  condition,  because  with  orthophoria  there  must, 
theoretically,  be  emmctropia,  and  experienced  examiners  know 
that  scarcely  one  eye  in  a  hundred  is  truly  emmetropic.  There- 
fore the  concomitant  of  ametropia,  as  will  be  seen  later  on,  is 
hetcrophoria,  for,  owing  to  the  distribution  of  the  ocular  nerves, 
a  single  impulse  would  seem  to  affect  both  the  intrinsic  and 
extrinsic  muscles  in  a  co-ordinate  manner,  unless  unconscious 
habits  have  been  formed  whereby  one  muscle  action  can  be 
suppressed  while  another  is  exerted,  even  though  the  nerve 
supply  is  the  same.  Now  this  involves  the  question :  What  is 
a  muscle  and  why  does  it  act?  So,  without  making  the  subject 
too  lengthy,  the  dictionary  may  be  briefly  quoted  as  stating  that 
a  muscle  is  an  organ  composed  of  contractile  fibres,  through 
the  contraction  of  ■ivJiich  bodily  movement  is  effected.  These 
muscles  are  classified  as  voluntary,  involuntary  and  mixed,  the 
voluntary  being  subject  to  the  will,  the  involuntary  acting  inde- 
pendent of  the  will,  and  the  mixed  combining  in  some  degree 
the  functions  of  both  the  others. 


INFLUENCE   OF    HABIT  lOI 

All  muscles  are  made  to  contract  by  means  of  nerves, 
and  a  nerve  is  described  as  a  cord-like  structure  composed  of 
delicate  filaments  through  which  sensations,  or  stimulatioti  im- 
pulses, are  transmitted  to  and  from  the  brain.  These  impulses 
being  an  expression  of  what  is  called  nervous  energy,  which 
represents  the  active  principle  of  organic  life,  this  nerve  action 
being  dependent  for  its  existence  upon  warmth,  food  and  the 
orderly  performance  of  the  functions  of  the  body.  It  will  be 
seen,  then,  that  this  question  is  much  like  the  ancient's  descrip- 
tion of  wisdom,  which  was  represented  as  a  serpent  with  its 
tail  in  its  mouth,  for  the  reasoning  resembles  a  circle,  no  be- 
ginning or  ending,  since  the  nervous  energy  seems  to  reproduce 
itself.  In  other  words,  it  takes  health  to  make  nervous  energy, 
and  nervous  energy  to  make  health. 

INFLUENCE  OF  HABIT.  As  before  referred  to,  ocular 
habits  of  adjustment  are  factors  to  be  reckoned  with  in  the 
adaptation  of  glasses,  for  it  is  not  difficult  to  understand  that 
if  an  eye  has  been  exerting  its  accommodation  for  many  years 
in  overcoming  an  error,  like  hypermetropia,  the  convergence 
has  had  to  form  special  habits,  too,  in  order  to  harmonize  with 
the  accommodation.  Then  when  glasses  are  given  for  the  cor- 
rection of  the  hypermetropia  it  follows  that  convergence  must 
be  re-educated  and  adapted  to  the  new  relationship. 

Prof.  William  James  says  that  "habit  has  a  physical 
basis"  and,  that  "the  moment  that  one  tries  to  define  what 
habit  is,  one  is  led  to  the  fundamental  properties  of  matter." 
He  further  says  that  the  phenomena  of  habit  in  living  beings 
are  due  to  the  plasticity  of  the  organic  materials  of  which  their 
bodies  are  composed,  and  that  the  philosophy  of  habit  at  bottom 
is  a  physical  principle  and  therefore  belongs  to  physics  rather 
than  to  physiology  or  psychology. 

Leon  Dumont  says :  "Every  one  knows  how  a  garment, 
after  having  been  worn  a  certain  time,  clings  to  the  shape  of 


I02  INFLUENCE   OF    HABIT 

the  body  better  than  when  it  was  new,  and  so  in  the  nervous 
system  the  impressions  fashion  for  themselves  appropriate 
brain  paths." 

Muscle  habits  are  really  brain  habits,  and  of  habits  in  gen- 
eral Professor  James  can  be  quoted  still  further,  he  says  :  "Habit 
is  what  keeps  us  all  within  the  bounds  of  ordinance,  and  saves 
the  children  of  fortune  from  the  envious  uprisings  of  the  poor. 
It  alone  prevents  the  hardest  and  most  repulsive  walks  of  life 
from  being  deserted  by  those  brought  up  to  tread  therein.  It 
keeps  the  fisherman  and  the  deck-hand  at  sea  through  the 
winter;  it  holds  the  miner  in  his  darkness,  and  nails  the  country- 
man to  his  log-cabin  and  his  lonely  farm  through  all  the  months 
of  snow ;  it  protects  us  from  invasion  by  the  natives  of  the 
desert  and  the  frozen  zone.  It  dooms  us  all  to  fight  out  the 
battle  of  life  upon  the  lines  of  our  nurture  or  our  early  choice, 
and  to  make  the  best  of  a  pursuit  that  disagrees,  because  there 
is  no  other  for  which  we  are  fitted,  and  it  is  too  late  to  begin 
again.  It  keeps  different  social  strata  from  mixing.  Already 
at  the  age  of  twenty-five  you  see  the  professional  mannerism 
settling  down  on  the  young  commercial  traveler,  on  the  young 
doctor,  on  the  young  minister,  on  the  young  counsellor-at-law. 
You  see  the  little  lines  of  cleavage  running  through  the  char- 
acter, the  tricks  of  thought,  the  prejudices,  the  ways  of  the 
'shop,'  in  a  word,  from  which  the  man  can  by-and-by  no 
more  escape  than  his  coat  sleeve  can  suddenly  fall  into  a  new 
set  of  folds.  On  the  whole,  it  is  best  he  should  not  escape. 
It  is  well  for  the  world  that  in  most  of  us,  by  the  age  of  thirty, 
the  character  has  set  like  plaster,  and  will  never  soften  again. 

"If  the  period  between  twenty  and  thirty  is  the  critical  one  in 
the  formation  of  intellectual  and  professional  habits,  the  period 
below  twenty  is  more  important  still  for  the  fixing  of  personal 
habits,  properly  so  called,  such  as  vocalization  and  pronuncia- 
tion, gesture,  motion,  and  address.  Hardly  ever  is  a  language 
learned  after  twenty  spoken  without  a  foreign  accent;  hardly 


INFLUENCE   OF    HABIT  IO3 

ever  can  a  youth  transferred  to  the  society  of  his  betters  un- 
learn the  nasality  and  other  vices  of  speech  bred  in  him  by  the 
associations  of  his  growing  years.  Hardly  ever,  indeed,  no 
matter  how  much  money  there  be  in  his  pocket,  can  he  even 
learn  to  dress  like  a  gentleman-born.  The  merchants  offer  their 
wares  as  eagerly  to  him  as  to  the  veriest  'swell,'  but  he  simply 
cannot  buy  the  right  things.  An  invisible  law,  as  strong  as 
gravitation,  keeps  him  within  his  orbit,  arrayed  this  year  as  he 
was  the  last;  and  how  his  better-clad  acquaintances  contrive  to 
get  the  things  they  wear  will  be  for  him  a  mystery  till  his 
dying  day. 

"The  great  thing,  then,  in  all  education,  is  to  make  our 
nervous  system  our  ally  instead  of  our  enemy.  It  is  to  fund 
and  capitalize  our  acquisitions,  and  live  at  ease  upon  the  inter- 
est of  the  fund.  For  this  we  must  make  automatic  and  ha- 
bitual, as  early  as  possible,  as  many  useful  actions  as  we  can, 
and  guard  against  the  growing  into  ways  that  are  Ukely  to  be 
disadvantageous  to  us,  as  we  should  guard  against  the  plague. 
The  more  of  the  details  of  our  daily  life  we  can  hand  over  to 
the  effordess  custody  of  automatism,  the  more  our  higher 
powers  of  mind  will  be  set  free  for  their  own  proper  work." 

The  influence  of  habit  upon  our  ocular  functions  is  very 
strong  indeed,  as  in  most  cases  we  are  able  through  muscular 
effort  to  adapt  ourselves  to  our  visual  necessities,  even  though 
we  unconsciously  pay  a  price  in  what  is  called  "nervous  strain." 
A  hypermetrope  in  accommodating  for  his  error  is  not  unlike 
a  man  in  walking  with  his  feet  turned  outward  at  too  great  an 
angle,  for,  while  both  are  possible  for  a  period  to  time,  yet  con- 
tinued effort  will  eventually  be  productive  of  bad  results. 
Habits  of  seeing  under  proper  refractive  and  muscular  adjust- 
ments should  be  acquired  by  all  at  as  early  an  age  as  will  prove 
practicable  for  a  person  to  wear  glasses. 

Figs.  52,  54  and  56  are  designed  to  diagrammatically  illus- 
trate the  relationship  between  accommodation  and  convergence 


104  INFLUENCE   OF   HABIT 

in  emmetropia,  hypermetropia  and  myopia,  while  Figs.  53,  55 
and  57  may  give  some  idea  of  the  nervous  adjustment  required 
to  meet  the  ocular  needs,  from  the  standpoint  of  innervation 
and  enervation. 

Fig.  52  is  intended  to  show,  by  means  of  converging  lines, 
the  normal  balance  in  an  emmetropic  eye  between  the  muscles 
governing  accommodation  and  those  controlling  convergence. 

Here  it  will  be  seen  that  the  harmony  between  these  two 
factors  necessary  to  binocular  vision  is  in  accord,  and  that  the 

Fig.  52. 

£MMET  RO  PI/\ 
o.s.  ■  ^"      ■ 


BALANCING    THE    ACCOMMODATION    AND    CONVERGENCE    IN 
EMMETROPIA. 

lines  representing  accommodation  and  convergence  meet  at  a 
common  point  on  another  imaginary  line  called  the  median, 
which  extends  forward  from  midway  between  the  two  eyes, 
the  innervation  of  course  being  directed  toward  the  internal 
rectus  and  the  ciliary  muscles  of  each  eye. 

^^S-  53  is  designed  to  show  a  pair  of  thermometer-like 
tubes  which,  for  convenience,  might  be  styled  a  neuromcter, 
these  tubes  being  filled  with  an  imaginary  vital  fluid  repre- 
senting the  nervous  energy  required  to  maintain  the  action  of 
accommodation  and  convergence.     The  darts  are  to  call  atten- 


INFLUENCE   OF   HABIT 


105 


tion  to  the  height  of  the  fluid  in  the  two  columns,  and  to  show 
the  relative  amount  of  nervous  expenditure  necessary  to  main- 
tain requisite  muscle  effort.  Thus  in  emmetrppia  the  darts 
seem  to  be  equal  and  indicate  that  whatever  the  proportionate 
relationship  really  is,  it  remains  a  quantity  that  can  be  con- 
sidered as  constant. 

In  Fig.  54  may  be  seen  the  disturbed  relation  between 
accommodation  and  convergence  which  would  take  place  in 
hypermetropia  if  the  innervation  was  normal,  as  shown  in  Fig. 

Fig.  53. 


U 


EQUAL   INNERVATION    NECESSARY   TO  BALANCE  ACCOMMODATION 
AND    CONVERGENCE    IN    EMMETROPIA. 


53,  Thus  esophoria  and  the  origin  of  convergent  strabismus 
can  be  surmised. 

In  Fig.  53  the  darts,  "A"  and  "C,"  show  that  binocular  vis- 
ion would  be  impossible  under  these  conditions,  and  so  individ- 
uals having  eyes  of  this  kind  must  learn  to  either  decrease 
convergence  or  increase  accommodation  in  an  independent 
manner.  This  relative  effort  is  shown  by  the  position  of  the 
darts  in  the  ncuronietcr,  Fig.  55,  the  nervous  impulse  here 
being  much  greater  for  accommodation. 

In  Fig.  56  the  lack  of  harmony  between  darts  "A"  and  "C" 
indicates  that  in  myopia  accommodation  must  be  decreased  or 
convergence  increased  before  the  two  can  be  brought  together. 


io6 


INFLUENCE   OF   HABIT 


Fig.  57  shows  a  relative  adjustment  of  innervation  to  which 
nature  undoubtedly  resorts  in  cases  of  this  kind. 

With  an  understanding  of  the  disturbance  in  innervation 
which  a  hypermetrope  or  myope  has  to  make  in  order  to  con- 

FiG.  54. 

_  HY  P£RM£TROP/A 

o.s. 


.       O.D.[ 


IMBALANCE  OF  ACCOMMODATION  AND   CONVERGENCE  IN   HYPER- 

METROPIA. 


Fig.  55. 


UNEQUAL  INNERVATION  REQUIRED  TO  BALANCE  ACCOMMODATION 
AND    CONVERGENCE   IN    HYFERMETROPIA. 


stantly  maintain  binocular  vision,  it  is  quite  easy  to  see  how 
readily  an  individual  can  form  habits  of  muscular  action  con- 
trolling accommodation  and  convergence  which  would  prove 
most  difficult  of  reformation.     And  this  leads  the  reasoner  to 


INFLUENCE  OF   HABIT 


107 


a  general  consideration  of  so-called  "spasms,"  "latent  errors," 
"muscular  insuMciencies,"  etc.,  etc. 

It  also  serves  to  emphasize  the  importance  of  keeping  errors 
of  refraction  under  constant  correction,  thereby  enabling  indi- 

FiG.  56. 

o.s."  ^^^ 


0.0 


imbalance  of  accommodation  and  convergence  in  myopia. 

Fig.  57. 


UNEQUAL  INNERVATION  REQUIRED  TO  BALANCE  ACCOMMODATION 
AND  CONVERGENCE  IN  MYOPIA. 

viduals  to  form  new  ocular  muscle  habits  which  will  be  in 
accord  with  standard  visual  requirements.  Then,  too,  it  will 
show  the  wisdom  of  postponing  the  adaptation  of  prisms  until 
after  old  habits  have  been  broken  up  by  altering  the  conditions 
responsible  for  them. 


I08  CILIARY    SPASMS 

CILIARY  SPASMS,  ETC.  In  arguing  against  the  use 
of  cycloplegics  some  optometrists  are  inclined  to  question  the 
frequency  of  spasms  and  latent  errors  and  to  contend  that  their 
importance  is  overestimated,  but  familiarity  with  static  and 
dynamic  skiametry  will  soon  prove  the  contrary.  Spasms  are 
defined  as :  "Involuntary  convulsive  contraction  of  muscles^ 
and  "convulsion,"  in  turn,  is  described  as  '^irregular  and  violent 
commotion."  Now,  this  latter  definition  might  perhaps  be  modi- 
fied a  little  and  thereby  convey  a  somewhat  better  understand- 
ing of  the  term  spasm,  as  it  is  used  here. 

Owing  to  the  contractile  quality  of  muscles,  they  can  only 
do  one  thing,  and  that  is  to  pull,  not  push.  Therefore,  when 
the  term  "violent  commotion"  is  used,  it  is  immediately  asso- 
ciated with  the  idea  of  a  rapid  and  intense  muscular  activity, 
which  resembles  the  seizures  of  epilepsy,  and  wrong  impressions 
are  apt  to  be  formed. 

As  before  stated,  spasms  can  be  of  two  kinds — the  steady 
and  the  vacillating.  So,  where  the  word  tonic  is  used  in  con- 
nection with  them,  they  are  to  be  associated  with  the  idea  of 
an  unconscious,  involuntary,  regular,  steady  and  persistent 
muscle  tension. 

Where  the  word  clonic  is  used,  however,  it  should  be  under- 
stood to  mean  unconscious,  involuntary,  irregular,  contracting 
and  relaxing  muscle  action,  which,  when  taken  in  connection 
with  the  so-called  accommodation  of  an  eye,  may  be  either 
rapid  or  slow  in  its  operation. 

The  term  tonic  spasm  of  accommodation,  as  understood 
to-day,  bears  a  close  resemblance  to  what  many  readers  of 
Bonders  are  led  to  infer  from  his  use  of  the  term  "latent"  in 
connection  with  hypermetropia,  for  the  word  "tonus,"  from 
which  the  word  "tonic"  is  derived,  signifies  an  involuntary 
condition  which  might  be  likened  to  increased  vigor  or  tone 
in  a  muscle  whereby  it  may  insist  on  doing  more  work  than 
is  really  intended  for  it.     This,  of  course,  is  alike  applicable 


^ 


CILIARY    SPASMS  IO9 

to  myopic  and  emmetropic  eyes,  though  not  occurring  with  the 
same  frequency  as  in  hypermetropic  ones. 

The  cause  of  these  spasms  is  also  a  varying  one.  In  hyper- 
metropia  the  constant  muscle  tension  required  in  order  to 
maintain  vision  is  no  doubt  a  pronounced  factor.  In  myopia 
and  in  emmetropia  an  uncontrollable  supply  of  nervous  energy 
actuating  the  muscles  is  probably  one  reason  for  their  invol- 
untary contraction.  Occupation,  too,  which  leads  to  the  for- 
mation of  muscle  habits,  is  undoubtedly  another  cause,  and  so 
quite  a  number  of  reasons  might  be  suggested.  The  work  of 
the  optometrist,  however,  deals  only  with  the  determination 
of  their  presence  and  the  estimation  of  their  strength  or  influ- 
ence on  the  refraction  of  an  eye. 

Reference  has  been  made  to  the  use  of  a  local  toxicant,' 
technically  termed  a  "cycloplegic,"  which  is  employed  to  par- 
alyze the  muscle  action  of  an  eye,  but  the  drawbacks  attendant 
upon  the  use  of  this  means  are  so  many,  both  from  a  practical 
as  well  as  a  theoretical  standpoint,  that  some  method  had  to 
be  devised  in  order  to  eliminate  the  guess  work  which  must 
necessarily  enter  into  all  cases  where  the  exact  refraction  of  an 
eye  at  its  reading  or  working  point  is  not  known.  And  by 
"exact  refraction"  is  meant  the  muscle  tonus,  or  muscle  inner- 
vation, which  constitutes  an  individual  factor  in  each  case. 

By  subjective  methods,  if  the  patient  is  of  sufficient  intelli- 
gence and  shows  the  proper  amount  of  interest  in  the  case,  a 
cross-examination  in  connection  with  other  tests  will  enable 
an  examiner  to  form  a  fairly  satisfactory  idea  of  the  range  of 
accommodation,  and  from  this  known  range  he  can  make  a 
close  estimate  as  to  the  strength  of  the  glasses  required.  But 
by  the  method  known  as  dynamicskiametry  a  more  certain 
estimate  can  frequently  be  arrived  at^  for  by  this  examination 
the  burden  of  judgment  is  shifted  from  the  shoulders  of  the 


no  CILIARY    SPASMS 

patient  to  those  of  the  examiner  who,  as  his  experience  in- 
creases, should  be  a  better  judge  of  his  patient's  needs  than 
the  patient  himself. 

In  the  dynamic  method  attention  has  been  called  to  the 
fact  that  where  the  muscles  controlling  accommodation  were 
heavily  taxed  it  was  easy  to  see  how  readily  they  might  be 
induced  to  surrender  any  excess  of  energy  which  they  had 
hitherto  concealed,  no  matter  whether  this  concealment  was 
total,  in  the  form  of  a  tonic  muscle  effort,  or  intermittent  in 
the  form  of  a  clonic  one. 

Attention  will  be  invited  in  another  chapter  to  the  advan- 
tages to  be  derived  from  the  use  of  mobile,  rather  than  of 
fixed,  lens  values,  and  this  may  serve  to  make  this  point  plainer, 
for  spasms  of  accommodation,  especially  of  the  clonic  variety, 
require  a  lens  action  which  will  in  a  measure  imitate  the  in- 
crease and  decrease  in  convexity  of  the  crystalline  lens  of  an 
eye  itself.  To  deal  successfully  with  spasms,  an  examiner 
must,  therefore,  use  some  means  which  will  enable  him  to 
make  his  lens  changes  in  a  gradual,  rapid  and  accurate  manner, 
and  at  the  same  time  operate  at  any  desired  distance  from  his 
patient.  x^ 

(Then,  too,  if  habits  are  to  be  broken  up,  the  patient  must     ^ 
be  required  to  make  some  refractive  adjustment  that  is  unusual,      J 
and  differing  from  the  manner  in  which  his  eyes  have  been   >/ 
generally  employed.  X 

Many  persons  with  uncorrected  hypermetropia  use  their 
eyes  as  little  as  possible  for  reading  or  near  work.  Their 
muscle  adjustment  for  distance,  however,  is  almost  a  constant 
quantity  during  their  waking  hours.  If  such  a  person  is 
young,  and  the  ocular  muscle  action  is  vigorous,  a  static  test, 
without  cycloplegia,  made  at  twenty  feet  is  very  likely  to  un- 
cover only   a   portion  of  the  error,   for  the  reason  that  the 


CILIARY    SPASMS  III 

accommodation  muscles  have  been  so  in  the  habit  of  exerting 
themselves  at  this  distance  that  when  lenses  are  supplied  which 
remove  the  necessity  for  this  exertion  these  muscles  seem  to 
refuse  much  of  the  assistance  offered  them. 

On  the  other  hand,  if  this  case  is  examined  skiascopically 
at  a  distance  nearer  than  that  of  the  usual  reading  point,  it 
will  be  observed  that  the  eye  will  now  accept  lenses  very  much 
stronger,  for  here  habit  is  not  such  a  factor,  and  under  the 
burden  of  increased  muscle  effort  the  accommodation  will 
readily  give  up  the  excess  tension  which  it  was  so  accustomed 
to  exert  for  distant  uses.  Thus,  habit  being  temporarily  broken, 
the  muscles  governing  accommodation  and  convergence  are 
more  likely  to  assume  standard  relations,  and  especially  so  if 
a  lens  system  is  used  which  permits  of  binocular  mobile  action. 

In  myopia,  particularly  in  those  cases  which  have  remained 
uncorrected  for  a  number  of  years,  the  accommodation  is 
likely  to  prove  disappointing  in  its  action  by  behaving  either 
spasmodically  or  quite  the  reverse.  For  this  reason  greater 
care  must  be  exercised,  when  measuring  these  cases,  to  employ 
corroborative  methods.  A  myopic  case  can  seemingly  be 
readily  changed  into  a  hypermetropic  one  by  over-correction 
of  the  error,  but  muscle  habits  formed  through  ordinary  occu- 
pations cannot  be  changed  in  a  minute,  and  this  fact  must  ever 
control  the  judgment  of  an  examiner  and  cause  him  to  adopt 
such  methods  and  measures  as  will  give  him  the  fullest  informa- 
tion regarding  the  requirements  of  each  and  every  case  that 
presents  itself. 

Of  the  two  forces,  accommodation  and  convergence,  the 
former  is  probably  the  controlling  one.  So-called  "muscular 
insufficiencies"  are,  therefore,  doubtless  the  result  of  inco- 
ordination between  the  ciliary  and  the  recti  groups.  If  the 
theories  as  illustrated  by  Figs.  52  to  57,  inclusive,  are  correct 
ones,  then  the  fallacy  of  adapting  prisms  for  the  purpose  of 
permanently  assisting  the  muscles  controlling  convergence   is 


112  CILIARY    SPASMS 

made  plain  for  many  cases,  for  where  the  error  of  refraction 
is  not  fully  corrected  it  is  logical  to  expect  that  the  muscles 
controlling  convergence  will  not  behave  in  accordance  with 
standards  which  are  applicable  only  in  emmetropia. 

Where  the  recti  muscles  are  mal-attached  to  the  eyeball, 
or  where  there  is  a  permanent  deficiency  in  the  amount  of 
their  innervation,  then  prisms  would  seem  to  be  indicated,  but 
experience  teaches  that  these  cases  are  rare.  It  is  wise,  then, 
for  an  examiner  to  correct  his  patient's  refraction  first  and 
wait  for  the  muscles  governing  accommodation  and  convergence 
to  adapt  themselves  to  the  new  order  of  things.  If  they  fail  to 
do  this,  and  the  examiner  is  sure  that  the  error  of  refraction 
is  fully  corrected,  then,  and  only  then,  is  he  warranted  in  the 
use  of  prismas,  unless  for  the  accomplishment  of  some  tempo- 
rary result. 

While  adduction,  abduction  and  sursumduction  offer  import- 
ant data  by  which  to  aid  an  examiner's  judgment,  they  are 
usually  of  little  avail  until  after  emmetropia  has  been  estab- 
lished and  maintained  long  enough  for  accommodation,  con- 
vergence and  innervation  to  have  ordinarily  acquired  a  habit 
indicative  of  normal  muscle  balance. 

To  make  these  points  plain  it  can  be  seen  that  if  the  rela- 
tive proportion  of  three  degrees  of  convergence,  or  one  meter 
angle,  to  one  diopter  of  accommodation  is  taken  as  a  standard 
of  estimation,  then  eyes  having  one  diopter  of  hypermetropia 
in  reading  at  a  distance  of  sixteen  inches  away,  which  calls 
for  two  and  a  half  diopters  more,  must  make  an  accommodative 
effort  equal  to  three  and  one-half  diopters  in  all. 

This  ciliary  action  would  call  for  a  harmonious  conver- 
gence equal  to  about  ten  degrees,  and  ten  degrees,  in  turn, 
would  call  for  a  reading  distance  of  eleven  inches  away,  thus 
showing  that  while  the  eyes  were  accommodating  for  sixteen 
inches  they  would  really  have  to  converge  to  a  point  five  inches 


CILIARY    SPASMS  II3 

nearer  in  order  to  use  a  standard  or  proportionate  amount  of 
nervous  energy ;  and  as  this  would  be  quite  impossible  without 
disturbing  binocular  vision,  hence  the  only  other  course  left  is 
for  the  innervation  of  the  convergent  muscles  to  be  correspond- 
ingly decreased. 

As  emmetropic  eyes  cannot  alter  their  co-ordinate  muscle 
action  without  previous  training,  it  would  seem  to  be  reason- 
able to  assume  that  ametropic  eyes  ought  also  to  require  an 
equal  time  and  training  in  order  to  enable  them  to  convert 
their  latent  errors,  or  those  due  to  habits  of  suppression,  into 
manifest  ones,  or  those  within  the  individual's  own  control. 

To  what  extent  habit  interferes  with  the  accuracy  of  static 
skiametry  must  be  left  to  the  imagination  of  those  examiners 
who  have  not  yet  had  opportunities  of  personal  observation. 
And  while  dynamic  skiametry  offers  a  marvelous  improvement 
in  estimating  the  true  refractive  errors  of  young  persons,  it,  too, 
is  frequently  interfered  with  by  this  same  disturbing  factor  of 
habit,  or  "individual  equation,"  as  it  is  sometimes  called. 

It  must  not  be  overlooked,  however,  that,  even  after  latent 
errors  have  been  determined,  and  spasms  unlocked,  it  is  not 
always  wise  to  endeavor  to  force  eye  muscles  to  accept  standard 
relationship  in  too  short  a  period  of  time,  for  while  it  is  true 
that  usually  the  best  results  are  obtained  after  emmetropia  and 
orthophoria  have  been  established,  yet  it  is  equally  true  that, 
in  some  cases,  it  is  better  to  ignore  a  small  spasm  and  permit 
the  muscles  to  work,  for  a  while,  in  excess  of  normal  re- 
quirements. 

This,  therefore,  indicates  that  optometric  findings  are  one 
thing  and  the  judgment  used  in  adapting  glasses  and  prisms  is 
quite  another.  For  with  the  experienced  examiner  it  often 
happens  that  in  youthful  cases  he  may  find  an  error  of  perhaps 
four  diopters  of  hypermetropia  by  the  dynamic  method,  and  yet 
correct  only  two  diopters  of  this  in  the  first  glasses  given, 
taking  several  months  of  time  in  order   to   educate   the   eye 


114  CILIARY    SPASMS 

muscles  up  to  a  normal  standard  where  they  can  bear  a  full 
correction  of  their  refractive  errors. 

The  making  of  the  original  examination  in  a  thorough  and 
reliable  manner  will  thus  be  seen  to  greatly  assist  an  examiner 
in  prognosticating  his  cases,  as  well  as  in  giving  advice  the 
correctness  of  which  will  be  borne  out  in  due  course  of  time. 

There  is  an  old  adage  which  says  that  "it  takes  a  long  time 
to  teach  old  dogs  neiv  tricks,"  and  the  reason  for  this  lies, 
perhaps,  in  the  fact  that  before  new  habits,  or  ^'tricks,"  can  be 
formed  the  old  ones  must  be  broken  up,  and  this  in  some  cases 
may  be  more  of  a  task  than  even  the  formation  of  the  new. 
Spasmodic  muscle  action,  while  unimportant  in  some  cases,  is 
quite  the  contrary  in  others,  so  that  the  wise  examiner  will  take 
no  chances,  but  proceed  to  thoroughly  master  all  of  his  cases. 
Any  unsatisfactory  results  that  may  occur  can  then  be  at- 
tributed more  to  faulty  judgment  than  to  a  lack  of  knowledge 
of  the  optical  and  correlated  intrinsic  and  extrinsic  muscle 
action  involved. 


CHAPTER  VII. 

Practice  of  Dynamic  Skiametry,  Its  Use  in   Measuring 
Regular  and  Irregular  Astigmia,  and  Its  Special 

Value  in  the  Objective  Estimation  of  Presbyopia 
AND  Sub-Normal  Accommodation,  Together  With  Its 
Relationship  to  Other  Methods  and  Tests. 

PRACTICE  OF  DYNAMIC  SKIAMETRY.  It  is  un- 
questionably true  that  no  other  one  instrument  in  the  arma- 
mentarium of  an  optometrist  requires  more  practice  to  success- 
fully master  than  does  the  skiascope,  and,  it  might  be  added 
that  the  dynamic  method  requires  much  greater  skill  in  order 
to  read  the  shadow's  action  than  does  that  of  the  static.  The 
reason  for  this  is  to  be  found  in  a  consideration  of  the  subject 
of  retinal  illumination,  for  it  is  well  known  that  the  shorter 
the  distance  between  the  light  source  and  the  patient's  eye  the 
larger  and  brighter  will  be  the  area  of  illumination  on  the 
fundus  of  the  eye  under  examination.  This,  taken  in  connection 
with  the  optical  laws  regulating  penumbra,  and  the  variation 
in  retinal  pigmentation,  together  with  size  of  ocular  pupils, 
added  to  light  stimulation,  will  show  why  the  nearer  a  shadow 
test  is  made  the  more  difficult  becomes  the  reading. 

If  it  was  not  for  the  erratic  relationship  that  frequently 
exists  between  accommodation  and  convergence,  and  for  the 
irregularities  existing  in  corneal  curvatures,  then  the  static 
method  would  be  the  best  to  use,  and  the  greater  the  distance 
it  was  employed  the  better  the  results  would  be.  But  ski- 
atnetry,  like  many  other  systems,  has  to  be  taken  as  it  is,  and 
not  as  the  operator  or  patient  would  like  to  have  it. 

Practice,  plenty  of  practice,  the  same  as  one  becomes  expert 


Il6  TRACTICE    OF   DYNAMIC    SKIAMETRY 

in  shooting  a  gun,  or  in  making  examinations  by  indirect 
ophthalmoscopy  is  the  only  way  in  which  an  examiner  can 
become  skillful  in  skiametry.  The  general  variation  in  appear- 
ance of  eyes  is  such  that  a  comprehensive  description  of  all 
kinds  is  almost  impossible,  the  student  must,  therefore,  see  for 
himself.  But  to  put  into  words  a  description  of  the  procedure 
necessary  in  making  an  examination  by  the  dynamic  method 
the  following  may  give  a  better  understanding. 

In  order  to  secure  as  favorable  a  fundus  reflex  as  possible, 
place  the  Hxatioti-stand  target  card  forty  inches  from  the  pa- 
tient's eyes  and  then  make  the  first  skiascopic  observation  from 
a  point  about  two  or  three  inches  to  the  left  of  this  card  and 
an  inch  or  so  nearer  the  patient.  If  motion  against  is  not 
present  then  add  plus  spheric  lenses  until  motion  against  occurs 
in  some  meridian.  The  strength  of  the  lens  next  zveaker  than 
the  one  that  just  causes  the  against  motion  is  the  one  that 
represents  the  error  for  this  distance  in  the  meridian  measured. 

If,  on  the  other  hand,  at  the  first  observation  an  against 
motion  is  noted,  then,  with  the  patient  still  looking  at  the 
fixation-stand  card,  the  examiner  is  to  advance  toward  the 
patient  until  a  zvith  motion  is  obtained  in  some  one  meridian. 
This  distance,  estimated  in  diopters,  less  the  i,  D.  of  accommo- 
dative myopia,  due  to  the  forty-inch  fixation,  will  represent  the 
true  myopia  for  the  meridian  measured,  and  if  astigmia  is 
present  all  the  meridians  will  not  measure  alike. 

After  this  first  estimation  of  the  error,  or  errors,  the  exam- 
iner is  to  place  the  estimated  correcting  lenses  in  position  on 
the  patient's  face  and  make  a  subjective  test,  after  which  he 
is  to  return  to  skiametry  again  and  make  another  examination 
at  a  reading  or  much  nearer  point  than  the  first  one  was  made, 
using  the  fixation  cards  on  his  bracket  skiascope.  The  changing 
back  and  forth  from  objective  to  subjective  and  from  subjective 
to  objective  will  be  seen  to  give  all  the  refractive  data  that  it  is 
possible  to  obtain,  after  which  the  use  of  other  instruments  and 


MEASURING  ASTIGMIA  BY  SKIAMETRY  II7 

methods  may,  or  may  not,  be  indicated,  as  their  necessity  is 
usually  determined  by  the  previous  findings. 

Two  typical  cases  may  possibly  make  these  points  plainer: 
Case  i.  Age  of  patient,  thirty  years.  Fixation,  forty  inches. 
Observation,  thirty-nine  inches.  Shadow  ivitli  the  mirror.  Can 
add  plus  I.  D.  before  reversal  occurs.  Subjective  test  also 
shows  I.  D.  of  hyperopia.  But  with  fixation  and  observation 
at  sixteen  inches,  a  total  of  plus  1.50  D.  can  be  added  before 
reversal  takes  place.  Same  result  is  obtained  when  fixation 
and  observation  are  at  thirteen  inches.  Case  2.  Age  of  patient, 
thirty  years.  Fixation,  forty  inches.  Observation,  thirty-nine 
inches.  Shadow  shows  against  the  mirror.  Reversal  takes 
place  at  twenty  inches  which,  after  deducting  i.  D.  for  the 
accommodative  myopia  at  forty  inches,  leaves  i.  D.  of  true 
myopia.  Subjective  test  calls  for  a  minus  1.50  D.  S.  lens. 
Fixation  and  observation  at  sixteen  inches  show  a  zvith  mo- 
tion with  a  minus  0.75  D.  S.  lens,  and  at  thirteen  inches  a 
minus  0.50  D.  S.  lens  is  the  weakest  one  a  ■with  motion  can  be 
obtained  with.  The  student  must  not  forget,  however,  that 
data  and  prescription  are  not  always  one  and  the  same. 

MEASURING  REGULAR  AND  IRREGULAR  AS- 
TIGMIA BY  SKIAMETRY.  "  The  variation  in  the  appear- 
ance of  astigmatic  eyes  is  often  baffling  to  the  skiametrist. 
Some  shadows  show  an  even  edge  that  makes  their  measure- 
ment most  easy,  while  others  scatter  and  re-form  several  times 
in  crossing  over  a  pupil.  The  cause  for  this  can  perhaps  be 
found  in  a  consideration  of  scar  tissue,  for  where  reliable  his- 
tory of  many  cases  of  this  kind  has  been  obtained  it  is  found 
that  in  childhood  the  patient  suffered  from  inflamed  eyes,  and 
the  sequela  was  the  irregularly  thickened  cortical  tissue  which 
manifests  itself  in  unequal  refraction. 

A  study  of  these  cases  with  the  skiascope  will  often  enable 
an  examiner  to  cope  with  those  which  at  first  seem  almost  hope- 


Il8  MEASURING   PRESBYOPIA  BY  SKIAMETRY 

less,  and  this  rule  holds  good  with  all  classes  of  skiametric 
cases,  no  matter  what  method  is  used.  The  skiametrist  must 
simply  perfect  his  skill  by  ample  practice. 

When  the  conditions  are  ideal  an  examiner  will  be  able 
to  note  a  sort  of  straight  edge  action  to  the  shadow.  If  the 
error  is  marked  then  this  edge  will  be  well  defined,  but  if  the 
error  is  slight  then  the  edge  will  be  difficult  to  note. 

In  those  cases  where  what  is  called  the  "scissors"  movement 
appears  an  examiner  will  observe  two  shadows  in  one  meridian, 
one  with  the  mirror  and  the  other  against.  This  is  frequently 
caused  by  making  the  observation  too  far  to  one  side  of  the 
line  of  fixation,  especially  where  the  correcting  lenses  used  are 
of  high  power. 

The  generally  accepted  theory  of  the  cause  of  the  "scis- 
sors" movement  attributes  it  to  the  crystalline  lens  being  slightly 
askew  in  its  capsule,  but  if  an  examiner  will  keep  the  lines  of 
observation  and  fixation  as  near  together  as  it  is  possible  and 
obtain  a  good  fundus  reflex  he  will  find  that  true  crystalline 
displacements  are  quite  rare. 

In  partially  opaque  corneas,  and  in  cases  of  cortical  cataract 
where  transparency  is  interfered  with,  an  examiner  will  often 
be  rewarded  through  results  obtained  by  careful  work  with 
his  skiascope.  Cataracts  in  process  of  development  can  often 
be  detected,  too,  long  before  the  vision  of  the  patient  is  per- 
ceptibly impaired.  The  spicula  in  the  crystalline  showing  trans- 
lucent upon  the  red  background  of  the  pupil,  and  especially  do 
they  appear  plain  when  mechanical  mydriasis  is  made  use  of. 

MEASURING  PRESBYOPIA  BY  SKIAMETRY. 
Presbyopia  is  usually  regarded  as  an  inilrmity,  rather  than  as 
an  error  of  refraction,  but  it  can  also  be  considered  in  the  latter 
light,  too,  for  research  proves  that  the  crystalline  changes  begin 
almost  at  birth  and  continue  all  through  life.  Loss  of  elasticity 
due    to    changes  in   density   and  to  production   of   an   altered 


MEASURING  PRESBYOPIA  BY  SKIAMETRY  1 19 

index  surely  indicate  refractive  variations,  and  as  the  only  dif- 
ference between  lenses  of  like  kind  is  variation  in  ray-bending 
power,  therefore  presbyopia  would  seem  to  rightfully  belong 
under  the  classification  of  refractive  anomalies,  just  as  much  as 
under  accommodative  anomalies. 

Presbyopia  is  the  one,  so-called,  "easy"  ocular  condition 
that  is  often  the  most  difficult  of  satisfactory  correction,  for  the 
reason  that  occupation,  illumination,  habit,  pupillary  distance 
and  innervation,  or  bodily  vigor,  are  all  factors  to  be  reckoned 
with.  Then,  if  combined  with  this  the  ignorance  and  stupidity 
of  many  patients  in  answering  questions  is  taken  into  consid- 
eration, it  is  easy  to  see  why  changes  in  reading  glasses  are 
so  frequent  when  "there's  nothing  the  matter  with  the  eyes." 

Up  to  the  time  of  the  development  of  the  dynamic  method 
of  practising  skiametry  there  was  no  known  method  of  estimat- 
ing presbyopia  in  an  objective  manner.  All  static  methods, 
whether  with  or  without  cycloplegia,  are  solely  for  determining 
the  refractive  condition  of  an  eye  while  its  muscles  are  in  a 
state  of  complete  relaxation,  therefore  the  static  method  gives 
no  definite  aid  in  presbyopia  whatsoever. 

Dynamic  skiametry  supplies  the  refractionist  with  a  method 
that  often  proves  of  the  very  greatest  aid  in  mastering  a 
troublesome  case,  as  it  enables  the  eyes  to  be  studied  at  all 
points,  near  as  well  as  distant,  this  study  being  directed  toward 
steadiness  of  convergence  and  accommodation,  both  of  which 
can  be  detected  through  the  use  of  a  skiascope  and  lenses.  As 
illustrative  of  this,  suppose  a  case  presents  itself  having  a 
history  of  discomfort  in  reading,  etc.,  the  patient  is  directed  to 
look  at  the  skiascope  Hxation-card  fourteen  inches  away  while 
plus  one-diopter  spheric  lenses  are  before  each  eye.  If  right 
eye  shows  a  with  motion  while  left  eye  is  against,  it  indicates 
either  an  error  of  refraction  or  an  unequal  innervation  of  the 
muscles  controlling  accommodation,  notwithstanding  that  at 
infinity  both  error  and  vision  seemed  alike  in  the  two  eyes.    The 


120  SUB-NORMAL  ACCOMMODATION 

use  of  the  mirror  at  this  distance  also  enables  the  detection  of 
any  deviation  in  convergence  of  either  eye  when  fixation  for 
this  point  is  maintained  for  a  considerable  time. 

It  is  conceded,  of  course,  that  it  takes  more  skiametric  skill 
to  measure  an  eye  at  fourteen  inches  than  it  does  at  forty,  but 
that  which  is  possible  for  one  examiner  is  also  possible  for 
another  with  equal  intelligence  and  perseverance.  Dynamic  ski- 
ametry  being  particularly  adapted  to  the  needs  of  those  who 
are  advanced  in  optometric  knowledge  and  skill. 

SUB-NORMAL  ACCOMMODATION.  In  comparatively 
recent  years  that  which  was  formerly  called  "latent"  hyperme- 
tropia  has  been  classed  as  an  early  or  sub-normal  accommoda- 
tion, and  practitioners  of  repute  are  now  adapting  bi-focal 
lenses  to  young  persons  with  great  success  in  some  cases. 

To  the  optometrist  it  matters  little  whether  the  patient's 
inability  to  see  nearby  objects  is  caused  by  latent  hypermetropia 
or  by  an  early  change  in  the  index  of  refraction  of  the  crys- 
talline, or  by  a  weakened  muscle  action,  what  he  needs  to  know 
is  the  true  condition  of  the  refraction  at  all  points,  near  and 
distant,  and  then  by  keeping  the  patient  under  observation  it 
can  be  determined  whether  the  case  is  one  requiring  the  aid  of 
the  family  physician  or  of  the  ophthalmic  specialist. 

As  in  presbyopia,  dynamic  skiametry  instantly  detects  a  lag 
in  accommodation,  and  if  this  "lag"  is  present  it  needs  looking 
after. 

A  case  is  reported  of  a  young  Miss,  fifteen  years  old,  who 
was  behind  in  her  school  work.  She  had  been  atropinised  and 
fitted  with  O.  U.  plus  i.  D.  S.  lenses  for  constant  use.  So- 
called  "retinoscopy,"  in  the  hands  of  an  optometrist  who 
thought  well  of  his  own  ability,  confirmed  the  findings  of  the 
oculist  who  prescribed  the  glasses.  Static  skiametry  also  con- 
firmed the  prescription  given.  Dynamic  skiametry,  however, 
showed  that  a  plus  3.   D.   S.   lens  was   indicated  at  thirteen 


OTHER   TESTS  121 

inches.  Plus  2.  D.  S.  lenses,  O.  U.  worn  for  a  month  did  not 
succeed  in  relaxing  any  more  than  the  original  correction  for 
infinity.  Bi-focals  of  plus  i.  D.  S.  upper  and  plus  3,  D.  S. 
lower  gave  almost  perfect  results  after  this  form  of  glass  had 
been  worn  a  few  weeks.  Adduction  and  abduction  were  both 
poor,  but  the  eyes  were  orthophoric.  If  dynamic  skiametry  had 
not  been  used  in  this  case  the  chances  are  that  it  would  have 
gone  the  way  of  many  others,  and  the  patient  allowed  to 
suffer  on. 

Perhaps  a  stronger  cycloplegic,  or  a  long  period  of  wearing 
fogging  lenses  would  have  revealed  more  latent  error,  but  the 
indications  were  that  this  was  a  case  of  what  is  termed  "pre- 
mature presbyopia"  or  "sub-normal  accommodation,"  and 
dynamic  skiametry  was  the  only  method  by  which  it  could  be 
intelligently  refracted. 

OTHER  TESTS.  It  may  do  no  harm  to  repeat  once 
more  that  no  one  optometric  test  is  the  "whole  thing,"  as  the 
urchins  say.  The  definition  of  the  word  optometry,  it  must  not 
be  forgotten,  is  eye-measuring.  That  of  skiametry  is  shadow- 
measuring,  and  as  the  word  ocular  means  eye,  it  Avill  therefore 
be  seen  that  ocular-skiametry  is  only  one  division  of  optometry, 
and  that  the  dynamic  method  constitutes  merely  a  sub-division. 

If  all  divisions  of  a  subject  bear  an  integral  relation  to  the 
whole,  then  dynamic  skiametry  is  but  one  means  for  obtaining 
data  which,  together  with  that  secured  by  other  methods,  con- 
tributes to  the  formulation  of  the  proper  prescription,  and 
"proper  prescription"  means  the  glasses  that  are  best  for  the 
patient  to  use.  Thus,  if  by  subjective  measurement  the  patient 
says  that  his  vision  is  improved  by  the  use  of  a  convex  spheric 
lens  of  two  diopters,  but  by  keratometry  a  mal-curvature  of  a 
half-diopter  of  the  cornea  is  shown,  and  by  dynamic  skiametry 
a  three-diopter  convex  spheric  is  called  for,  then  it  may  be  wise 
to  prescribe  a  two  and  one-half  sphere,  especially  if  the  patient 


122  OTHER   TESTS 

has  been  wearing  a  partial  correction  and  gives  a  history  of 
eye-strain. 

It  is  the  combination  of  important  factors  in  a  given  case 
that  often  makes  success  possible.  Blind  adherence  to  any  one 
test,  or  method,  is  no  doubt  responsible  for  many  optometric 
failures.  Duction  tests  of  the  muscles  give  data  that  have  great 
influence  in  determining  the  strength  of  lenses  to  be  prescribed, 
even  though  prisms  are  not  used,  and  where  heterophoria  is 
present  the  data  secured  by  means  of  dynamic  skiametry  may 
often  save  the  prescribing  of  prisms. 

The  aim  of  the  thorough-going  optometrist  should  be  to 
determine  as  carefully  as  possible  the  true  condition  of  his 
patient's  eyes.  And  this  involves  many  tests  in  some 
cases  and  few  in  others,  for  a  case  of  simple  presbyopia,  with 
standard  vision  and  no  history  of  discomfort,  does  not  need  the 
time  nor  the  many  tests  that  are  indicated  where  the  ametropia 
is  complex  and  the  history  of  general  health  and  nervousness 
poor. 

Of  course  the  treatment  of  impaired  health  of  a  patient  is 
foreign  to  the  service  that  an  optometrist  is  generally  consulted 
for,  but  a  "poor  history"  forms  data  that  has  an  indirect  bear- 
ing upon  all  optometric  cases,  so  the  wise  examiner  acquaints 
himself  with  all  tests  and  methods  that  will  aid  him  in  the  for- 
mation of  correct  judgment,  for,  after  all,  it  is  this  "judgment" 
which  makes  one  succeed  where  another  fails. 

Perhaps  one  of  the  hardest  strains  a  new  method  has  to 
stand  is  the  extravagant  claims  made  for  it  by  enthusiasts. 
Take  the  keratometer  for  instance,  a  very  valuable  instrument 
but  often  most  unreliable  where  its  findings  are  blindly  adhered 
to.  One  great  mistake  made  by  many  practitioners  of  op- 
tometry is  that  they  do  not  take  their  profession  seriously 
enough.  It  seems  so  easy  to  use  a  few  instruments,  ask  a  ques- 
tion or  two  and  then  form  snap  judgment  as  to  a  patient's 


OTHER   TESTS  1 23 

requirements,  therefore  it  is  little  wonder  that  this  field  attracts 
to  it  many  incompetents. 

As  optometry  develops,  however,  it  is  hoped  that  the  general 
public  will  grow  wiser  and  learn  to  reward  those  who  give  the 
time  and  make  the  effort  to  fully  master  each  and  every  detail 
that  has  direct  and  indirect  bearing  upon  the  practice  of 
optometry  in  its  larger  sense. 


CHAPTER  VIII. 

Illustrative  Cases^  Showing  the  Comparative  Value  of 
Static  and  Dynamic  Skiametry  in  Patients  of  Dif- 
ferent Ages,  Occupation  and  General  Physical 
Condition. 

ILLUSTRATIVE  CASES.  The  expression  "Figures 
talk"  is  especially  applicable  in  describing  the  relative  merits  of 
static  and  dynamic  methods  in  practising  ocular  skiametry. 
Space,  therefore,  will  here  be  devoted  to  descriptions  of  various 
cases  for  the  purpose  of  emphasizing  points  already  alluded 
to,  and  of  incidentally  calling  attention  to  the  influence  of 
occupation  and  the  importance  which  attaches  to  the  condi- 
tion of  the  patient's  general  health.  All  the  examinations 
referred  to  were  made  without  the  aid  of  cycloplegics,  conse- 
quently the  static  test  mentioned  is  the  non-toxic  kind. 

CASE  A. 

Master  S.,  age  7.  In  school.  Health,  seemingly  good; 
O.  S.  shows  slight  convergent  squint. 

Vision  =  O.  D.  20/20.    O.  S.  20/100.  • 

Static  test  =  O.  D.  -f  2.50  D.  S.    O.  S.  -|-  3.  D.  S. 

Dynamic  test  at  forty  inches  =  O.  U.  -f  3.50  D.  S. 

Dynamic  test  at  twenty  inches  r=  O.  U.  -f-  4,  D.  S. 

Dynamic  test  at  thirteen  inches  =  Unsatisfactory. 

Trial  case  test  =  O.  D.  -f  2.  D.  S.    O.  S.  +  3.  D.  S. 

Vision  =  O.  D.  20/20.    O.  D.  20/80. 

Formula  given  =  0.17.-}-  3.  D.  S.  for  constant  use,  with 

instructions  to  return  in  one  year. 


ILLUSTRATIVE    CASES  I25 

Two  years  later    O.  U.  -f  3.50  D.  S.  was  readily  accepted. 

No  squint. 

Vision  =r  O.  D,  20/20.    O.  S.  20/40. 

CASE  B. 

Master  W.,  age  11.     Health  not  rugged.     Inability  to  see 
blackboard. 

Vision  =  O.  U.  20/100.    Static  test  =  O.  U.  —  i.  D.  S. 

Dynamic  test  at  13  inches  =  O.  U.  —  0.50  D.  S. 

Trial  case  test  :=  O.  U.  —  1.25  D.  S. 

Vision  =  20/20  in  both  eyes. 

Formula  given  =:  O.  U.  —  0.50  D.  S.  for  constant  use. 

Instructed  to  return  in  three  months. 

Six  months  later  vision  O.  U.  =  20/20  with 
O.  D.  —  0.75  —  D.  S. 
O.  S.  —  0.75  —  D.  S. 


CASE  C. 

Miss  N.,  age  16.    In  school.    Health  fair.    Headaches. 

Vision  =  O.  U.  20/30. 

Static  test  =  O.  U.  +  0.50  D.  C.  90°. 

Dynamic  test  at  16  inches,  same. 

Trial  case  test  =  O.  U.  —  0.50  D.  C.  180°. 

Vision  =  20/20  in  both  eyes. 

Formula  given  =  O.  U.  +  0.50  D.  C.  90°. 

Vision  =  "misty." 

Instructed  to  use  at  study,  and  oftener  if  more  comfortable. 
Later  on  she  reported  "no  headaches,"  and  vision  was  found 
to  be  20/20  with  glasses. 


126  ILLUSTRATIVE    CASES 

CASE  D. 

Mr.  G.,  age  20.    In  college.    Reports  his  health  good.    No 
discomfort,  but  "can't  see  at  a  distance." 

Vision  =z  O.  U.  20/200. 

Static  test  =  O.  U.  —  2.50  D.  S. 

Dynamic  test  at  40  inches  =  O.  U.  —  2,  D.  S. 

At  16  inches,  about  the  same. 

Trial  case  test  =  O.  U.  —  2.75  D.  S. 

Vision  =r  20/20  in  both  eyes. 

Formula  given  =  O.  U.  —  2.  D.  S.  for  constant  use. 

Instructed  to  return  if  he  had  any  further  trouble.    No  report. 

CASE  E. 

Mr.  S.,  age  24.    Mechanic.    Something  of  an  athlete ;  com- 
plains of  headache. 

Vision  O.  U.  =  20/20. 

Static  test  O.  U.  =  +  1.25  D.  S.  C  +  0.25  D.  C.  90°. 

Dynamic  test  at  13  inches  == 

O.  U.  =  -I-  2.  D.  S.  C  +  0.25  D.  C.  90°. 

Trial  case  test  O.  U.  =  +  i.  D.  S.  C  +  0.37  D.  C.  90°. 

Vision  =  20/20. 

Formula  given  O.  U.  =  +  i.  D.  S.  C  +  0.25  D.  C.  90°. 

Advised  to  return  in  one  year,  which  he  did,  and  was  given 

O.  U.  =  +  1.50  D.  S.  C  +  0.25  D.  C.  90°. 

Advised  to  return  again  within  two  years. 

CASE  F. 

Miss  F.,  age  26.     Seamstress.     General  health  not  good. 
"Weak  eyes." 

Vision  =  O.  D.  20/40.    O.  S.  20/80. 
Has  been  using  O.  U.  +  I.  D.  S. 


ILLUSTRATIVE  CASES  12/ 

Static  test  = 

O.  D.  4-  0.50  D.  S.  C  +  2.  D.  C.  90°. 
O.  S.  +  2.  D.  S.  C  +  2.  D.  C.  105°. 
Dynamic  test  at  40  inches  = 
O.  D.  -f  I.  D.  S.  C  +  2.  D.  C.  90°. 
O.  S.  +  3.  D.  S.  C  +  2.  D.  C.  105°. 
Dynamic  test  at  20  inches  = 
O.  D.  +  1.50  D.  S.  C  +  2.  D.  C.  90°. 
O.  S.  -f  3.  D.  S.  C  +  2.  D.  C.  105°. 
Dynamic  test  at  13  inches  =  Sam' 
Kcratometer  =  O.D.  2.  D.go°.    O.  S.  2.  D.  110°. 
(Note  difference  in  axis  of  O.  S, 
Trial  case  test  = 

O.  D.  +  0.25  D.  S.  C  +  2.  D.  C.  90°. 
O.  S.  +  1.50  D.  S.  C  +  2.  D.  C.  105°. 
Vision  =  O.  D.  20/20.    O.  S.  20/40. 
Formula  given  = 

O.  D.  +  I,  D.  S.  C  +  2.  D.  C.  90°. 
O.  S.  +  2.50  D.  S.  C  +  2.  D.  C.  105°. 

Instructed  to  wear  constantly  and  to  "never  mind  if  distant 
objects  are  a  trifle  blurred  for  a  few  weeks."  Returned  in  a 
week  with  a  history  of  occasional  discomfort.  Gave  advice  to 
persevere.  Returned  in  four  months  with  a  broken  lens  and 
wanted  a  new  one  "immediately."  Glasses  were  very  satis- 
factory.   Vision  =  O.  D.  20/20.    O.  S.  20/40. 

CASE  G. 

Mr.  C.,  age  29.  Bookkeeper.  Reports  health  good  when 
not  working  too  hard.  Eyes  and  head  "feel  bad"  afternoons. 
Has  been  wearing  glasses  for  three  years  of  the  following 
formula : 

O.  D.  —  I.  D.  S.  C  +  2.  D.  C.  75°. 
O.  S.  —  I.  D.  S.  C  +  1-50  D.  C.  105°. 


128  ILLUSTRATIVE  CASES 

Vision  with  present  glasses  =  O.  U.  20/30. 

Fundus  reflex  very  poor. 

Keratometer  shows  =  O.  D.  2.  D.  axis  75°.  O.  S.  2.  D.  axis  105°. 

Dynamic  test  at  thirteen  inches,  with  trial  lenses,  shows  the 

myopic  quantity  to  be  only  0.50  D.  in  both  eyes. 

Trial  case  test  = 

O.  D.  —  I.  D.  S.  C  +  2.  D.  C.  75°- 

O.  S.  —  I.  D.  S.  C  +  2.  D.  C.  105°. 

Vision  =  20/30. 

Formula  given  = 

O.  D.  —  0.50  D.  S.  C  +  2.  D.  C.  75°. 

O.  S.  —  0.50  D.  S.  C  +  2.  D.  C.  105°. 

Vision  =  "Foggy." 

Report  received  in  two  weeks:  "All  right  now." 

CASE  H. 
Mr.  R.,  age  34.    Grocer.    History  of  health  unsatisfactory. 
Vision  poor  for  past  few  months. 

Present  vision  =  20/80  in  both  eyes. 

Static  test  = 

O.  D.  4-  I.  D.  S.  C  +  0.50  D.  C.  180°. 

O.  S.  +  I.  D.  S.  C  +  0.50  D.  C.  180°. 

Dynamic  tests,  at  40  and  16  inches,  about  the  same.    Trial  case, 

about  the  same. 

Optical  correction  no  material  aid  to  vision.  Ophthalmo- 
scope shows  pale  discs.  Close  questioning  leads  to  conclusion 
that  it  is  a  probable  case  of  nicotine  poisoning,  due  to  immod- 
erate smoking  aggravated  by  the  moderate  use  of  alcohol.  Gave 
no  glasses.    Advised  to  consult  an  oculist  first. 

CASE  J. 

Miss  B.,  age  38.  Stenographer.  Says  health  is  good  except 
for  headaches. 


ILLUSTRATIVE  CASES  1 29 

Vision  =  O.  U.  20/20. 

Static  test  =  O.  U.  +  0.50  D.  S. 

Dynamic  tests  at  40  and  16  inches  =  O.  U.  -|-  0.75  D.  S. 

Trial  case  test  =  O.  U.  +  0.25  D.  S. 

Vision  =  20/20  trifle  "hazy." 

Formula  given  =1  O.  U.  +  O-50  D.  S. 

For  reading  and  near  work.     Good  report. 

CASE  K. 

Mrs.  A.,  age  41.  Has  household  cares  only.  General  health 
none  too  good.  Complains  of  inability  to  see  to  thread  her 
needle  and  do  fancy  work.    No  headaches. 

Vision  =  O.  U.  20/20. 

Dynamic  tests  at  40  and  16  inches  =  O.  U.  +  i.  D.  S. 

Trial  case  test  =  O.  U.  +  0.75  D.  S. 

Vision  =  20/20. 

Formula  given  =  -{-  i.  D.  S.  for  both  eyes. 

Instructed  to  use  for  near  work.     No  report. 

CASE  L. 
Mrs.    L.,   age  46.     Housekeeper.     Health   appears  good. 
Difiiculty  in  reading.     No   headache. 
Vision  r=  O.  U.  20/20. 
Static  test  =  O.  U.  +  0.25  D.  C.  90°. 

Dynamic  test,  at  40  inches,  about  the  same.     Trial  case,  about 
the  same. 

Dynamic  test  at  15  inches  =  -{-  i.  D. 

Formula  given  =  O,  U.  +  i.  D.  S.  C  +  0.25  D.  C.  90°  for 
reading,  etc.    No  report. 

CASE  M. 
Mr.  D.,  age  52,     Court  stenographer.     Health  seemingly 
good.     Never  has  had  any  glasses   that  proved  quite   satis- 
factory. 


130  ILLUSTRATIVE  CASES 

Vision  r=  O.  U.  20/80.    Dynamic  test  at  50  inches  = 

O.  D.  +  1.25  D.  S.  C+  0.25  D.  C  135°. 

O.  S.  +  1.25  D.  S.  C  +  0.25  D.  C.  90°. 

Trial  case  test,  the  same.    Vision  =  O.  U.  20/30. 

Presbyopia  r=  2.25  D.    Gave  bi-focals. 

Reported  in  sixty  days  that  vision  was  good  but  glasses  did 

not  seem  quite  right.    "Guessed"  he  was  working  too  hard. 

Re-examination  by  dynamic  test  at  30  inches  = 

O.  D.  +  1.50  D.  S.  C  +  0.25  D.  C.  120°. 

O.  S.  +  1.75  D.  S.  C  +  0.25  D.  C.  80°. 

Vision  =  O.  U.  20/20. 

Presbyopia  =  2,  D. 

Reported  in  six  months  "O.  K.  now,  'twas  the  glasses  after  all." 

CASE  N. 

Mr.  O'B.,  age  55.    Driver.    Health  good.    "Can't  see."' 

Vision  =  O.  U.  20/80.    Static  test  =  O.  U.  +  1.50  D.  S. 

Presbyopia  =  2.50  D. 

Trial  case  test  =  O.  U.  +  i-50  D.  S. 

Vision  =z  20/20. 

Formula  given  =  O.  U.  +  4-  D.  S.  for  reading.    Would  not 

wear  distance  correction. 

No  report. 

CASE  O. 

Mr.  E.,  age  59.  Tailor  and  cutter.  Health  good.  Working 
distance  about  twenty  inches  away.  Present  glasses  are  -|-  3* 
D.  S.  for  both  eyes,  and  are  not  very  satisfactory. 

Vision  =  O.  D.  20/30.    O.  S.  20/100. 

Static  test  = 

O.  D.  4-  0.50  D.  S. 

O.  S.  4-  I.    D.  S.  +  I.  D.  C.  180°. 


ILLUSTRATIVE  CASES  I3I 

Keratomctcr  shows  no  corneal  mal-curvature  in  either  eye. 
Trial  case  test,  same  as  static  test. 

Vision  =  O.  D.  20/20.     O.  S.  20/40. 

Presbyopia  at  working  distance  =  2.  D. 

Presbyopia  at  reading  distance  =  2.75  D. 

Formula  for  working  glasses  = 

O.  D.  +  2.50  D.  S. 

O.  S.  +  3.      D.  S.  +  I.  D.  C.  180°. 

Formula  for  reading  glasses  = 

O.  D.  +  3.25  D.  S. 

O.  S.  +  3.75  D.  S.  +  I.  D.  C.  180°. 

Instructed  to  return  if  not  satisfactory.     Xo  report. 

CASE  P. 

Mrs.  M.,  age  62.     Occupation   (?).     Health   (?).     Looks 
well. 

Vision  less  than  20/200  in  both  eyes. 

Static  test :  First  attempt,  no  retinal  reflex.    Without  skiameter 
the  mirror  shows  small  pupils  and  slow  plus  movement.    With 
skiameter,  lenses  being  set  to  enlarge  the  pupils,  better  move- 
ment is  obtained   and  long,   narrow,   spike-like  patches  show. 
Error  about  -|-  4.  D.  S.  in  both  eyes. 
Trial  case  test  =  O.  U.  -j-  3.50  D.  S. 
Vision  =  O.  D.  20/40.    O.  S.  20/60. 
Presbyopia  =  3.  D. 

Ophthalmoscope  shows   slight  cortical  cataracts. 
Gave  formulas :  Distance  =  O.  U.  -|-  3.50  D.  S. 
Reading  =  O.  U.  +  6.50  D.  S. 

With  instructions  to  be  sure  and  have  a  strong  light  coming 
over  shoulder  when  reading  or  sewing.  Sent  letter  to  family 
physician. 


132 


ILLUSTRATIVE  CASES 


CASE  Q. 

Mr.  McE.,  age  67.  Health  fair.  Retired.  Now  using 
glasses  -\-  4.  D.  S.  for  reading;  wonders  if  they  can  be  im- 
proved. 

Vision  =  O.  U.  20/80,  which  is  improved  by  partially  closing 
the  eyelids.  Static  test  =  O.  U.  -|-  i.  D.  S.  Trial  case  test  the 
same.  Vision  =  O.  U.  20/30.  Presbyopia  =:  -j-  3.  D.  S. 
Formula  for  distance  =  +  i.  D.  S.  Advised  to  continue  with 
present  reading  glasses  and  to  increase  his  illumination  when 
using  his  eyes  for  near  purposes.     No  report. 

Note. — According  to  Bonders  the  near  point  of  distinct  vision 
in  an  emmetropic  eye  is  as  follows : 

At  10  years  of  age  it  is     2^  inches  away. 


20      " 

'     "     "    -     4 

30    " 

.     .     .    .     ^y 

40    " 

•     "     "    "    9 

50    " 

'     "     "    "  16 

60    " 

'     -    "    "  40 

To  illustrate  in  fuller  detail  the  workings  of  dynamic  ski- 
ametry,  let  the  following  case  be  analyzed. 

Mr.  H.,  age  25.  Contractor's  timekeeper.  Leads  outdoor 
life.  General  health  excellent.  Complains  of  occasional 
headache. 

Vision  =  O.  U.  20/20.  Static  test  =  O.  U.  +  1.25  D.  S. 
Dynamic  test  at  13  inches  =  0.11.4-  2.  D.  S. 
Trial  case  test  ^  O.  U.  +  i.  D.  S.    Vision  =  20/20. 

By  reference  to  Fig.  54,  it  will  be  seen  that  when  his  accom- 
modation and  convergence  each  receive  an  equal  amount  of 
innervation,  the  convergence  will  be  greater  than  the  accommo- 
dation, and  binocular  confusion  will  result,  thus  giving  rise  to 
esophoria  unless  the  innervation  is  altered  in  some  way  so  as 


ILLUSTRATIVE  CASES  133 

to  produce  the  condition  called  forJiby  Fig.  55,  where  the 
innervation  for  accommodation  is  in  excess  of  that  for  con- 
vergence. A  test  of  his  extrinsic  muscles,  however,  shows  a 
manifest  orthophoria  without  glasses. 

Now  what  are  the  deductions  to  be  drawn  from  this  case? 
Twenty-five  years  of  daily  use  of  the  eyes  without  glasses  has 
established  a  habit  of  adjustment  whereby  the  standard  rela- 
tionship between  accommodation  and  convergence  has  been  re- 
placed by  a  condition  in  which  convergence  has  given  way  a 
little,  otherwise  esophoria  would  have  manifested  itself. 

The  static  test  shows  a  reversal  of  the  shadow  when  over  one 
and  a  quarter  diopters  of  convex  lens  power  are  added.  This 
is  in  addition,  of  course,  to  the  quantity  necessary  to  create 
the  artificial  myopia.  Thus  proving  that  hahit  has  not  mastered 
quite  all  of  the  error,  as  the  accommodation  readily  accepts 
partial  assistance  and  relaxes  its  muscle  tension  as  much  as 
five-eighths  of  the  full  ametropia  present.  The  remaining  three- 
eighths  of  the  total  error  can  be  called  latent,  but  in  reality  it 
represents  a  tonic  spasm,  a  knowledge  of  the  presence  of  which 
materially  aids  an  examiner  in  the  formation  of  his  judgment 
and  in  the  advice  and  prognosis  he  is  enabled  to  give  a  patient. 

To  determine  the  amount  of  tonic  spasm  present  in  a  case, 
such  as  the  one  under  consideration,  it  will  be  necessary  to 
resort  to  the  dynamic  method  which  calls  for  a  pronounced 
exertion  of  the  patient's  accommodation. 

An  emmctrope  twenty-five  years  of  age  is  supposed  to  have 
about  eight  diopters  of  amplitude  of  accommodation.  The  near- 
est point  of  distinct  vision  is  then  five  inches  away  from  the 
eyes.  A  dynamic  test  made  at  thirteen  inches  calls  for  an  ac- 
commodation equal  to  three  diopters.  The  patient's  error  being 
two  diopters,  it  follows  that  a  total  ocular  muscle  exertion  equal 
to  five  diopters  is  necessary  in  order  to  enable  the  patient  to  dis- 
tinctly read  small  letters  on  a  card  whose  distance  away  is  the 
same  as  that  of  the  examiner's  mirror. 


134  ILLUSTRATIVE  CASES 

More  than  five  diopters  of  accommodative  effort  can,  of 
course,  be  exerted  by  the  patient  in  this  case.  Yet  this  amount 
will  generally  be  found  quite  sufficient  to  break  up  any  tonic 
spasm,  or  habit  of  muscle  exertion,  that  may  have  been  formed. 
Five  diopters  less  three  diopters  leaves  two  diopters,  and  a  lens 
quantity  of  this  strength  should  reverse  the  shadow  by  the 
dynamic  test  under  these  conditions. 

If  the  test  had  been  made  at  twenty  inches,  then  four  diop- 
ters would  represent  the  total  muscle  effort  called  for.  If  at 
ten  inches,  then  six  diopters  would  be  the  full  accommodation 
needed.  The  difference  between  these  amounts  and  that  re- 
quired to  maintain  normal  relationship  between  accommodation 
and  convergence  at  whatever  distance  the  test  is  made  will 
show  at  once  in  the  lens  quantity  required  to  reverse  the 
shadow,  provided  the  eyes  are  examined  in  a  semi-binocular 
manner,  namely,  first  one  eye  and  then  the  other,  alternating  fre- 
quently so  as  to  insure  an  equality  of  visual  fixation. 

One  point  which  seems  to  puzzle  many  examiners  who  take 
an  interest  in  making  theory  substantiate  practice  is  to  under- 
stand why  an  emmetropic  eye  when  under  an  accommodative 
tension  of  three  diopters  at  thirteeen  inches,  will  not  relax  to 
two  diopters  when  one  diopter  of  assistance  is  offered  it.  The 
answer  to  this  query  probably  lies  in  a  better  understanding  of 
muscular  co-ordination  and  innervation,  for,  as  stated  in  earlier 
chapters,  the  eyes  of  a  healthy  person,  free  from  coercion, 
cannot  converge  without  accommodating,  nor  can  they  accom- 
modate without  converging.  And  this  co-ordinate  relationship 
will  respond  to  approximate  standards  unless  long-standing 
abnormal  requirements  have  induced  irregular  habits.  In  this 
latter  case  refractive  measurements  must  be  taken  in  such  a 
manner  as  to  estimate  the  real  influence  of  these  habits  by  mak- 
ing the  eyes  work,  for  the  time  being,  in  a  manner  as  far 
removed  from  old  beaten  paths  as  possible. 


ILLUSTRATIVE  CASES  135 

Now  another  case  will  be  cited  in  order  that  the  details  of 
skiametric  procedure  may  be  accentuated. 

Mr.  Z.,  age  thirty-five,  occupation  watchmaker.  Has  been 
studying  optics  for  two  years.  States  that  he  has  fitted  himself 
with  O.  U.  —  0.50  D.  S.  C  —  0.75  D.  C.  axis  i8o°,  that  his 
vision  without  glasses  is  O.  D.  =  15/30  O.  S.  =15/20,  and 
that  he  has  four  degrees  of  esophoria. 

As  the  above  information,  excepting  the  age,  is  supplied 
after  the  examination  is  finished,  the  examiner,  of  course,  pro- 
ceeds in  the  usual  manner  and  directs  the  patient  to  look  at  the 
letters  on  a  fixation  stand  card  situated  fifty-three  inches  dis- 
tant. In  an  observation  made  at  forty  inches  the  examiner  finds 
that  in  the  right  eye  there  is  a  fairly  distinct  edge  to  the  shadow 
and  that  it  points  a  little  to  the  left  of  the  vertical  meridian. 
Adding  convex  lens  quantity  it  is  found  that  one  diopter  is 
needed  to  reverse  the  shadow  in  the  horizontal  meridian,  and 
that  in  the  vertical,  with  no  lens  power  added,  the  motion  is  a 
trifle  against  the  mirror.  With  the  patient  still  looking  at  the 
fixation  card  fifty-three  inches  away  the  examiner  finds  that 
he  must  advance  his  mirror  ten  to  fourteen  inches  nearer  to  his 
patient  before  he  obtains  a  reversal  of  the  shadow  in  this  me- 
ridian. So  he  notes  on  his  examination  blank  "O.  D.  —  0.25 
D.  S.  C  -f  I.  D.  C.  axis  105." 

In  the  left  eye  the  horizontal  motion  is  reversed  with  a  half- 
diopter  convex  lens  quantity.  In  the  vertical  meridian  there 
is  a  motion  zvitli  the  mirror,  when  the  examiner  is  forty  inches 
away.  Adding  even  a  slight  convex  lens  power  stops  it.  The 
axis  seems  to  be  about  fifteen  degrees  to  the  temporal  side  of 
the  head.  The  examiner  notes  "O.  S.  -f  0.50  D.  C.  axis  75." 
Corroborating  subjectively,  it  is  found  that  vision  O.  U.  20/20, 
a  trifle  "misty,"  can  be  secured  with  O.  D.  —  0.50  D.  S.  C  + 
0.75  D.  C.  axis  105  and  O.  S.  -|-  0.25  D.  C  axis  75.  Patient 
reads  well  with  this  correction,  and  —  0.50  D.  S.  or  -f-  0.50 
D.  S.  added  in  a  binocular  way  offers  no  aid.     Corroborating 


136  ILLUSTRATIVE  CASES 

skiametricaUy  again  with  the  full  correction  on,  it  is  found  that 
a  quarter-diopter  convex  lens  reverses  the  shadow  in  all  merid- 
ians when  the  patient  looks  at  the  brow  card  on  the  examiner's 
mirror,  no  matter  whether  its  distance  be  twenty  or  forty 
inches  away.  With  the  quarter-diopter  convex  lens  power 
removed,  the  shadow  shows  a  suggestion  of  a  movement  with 
the  mirror,  at  the  same  distances  of  twenty  and  forty  inches 
away.  The  above  formula  is  then  ordered  and  the  patient  is 
instructed  to  wear  the  glasses  as  much  as  possible  and  to  report 
in  a  month. 

In  analyzing  this  case  the  occupation  of  the  patient  is  borne 
in  mind  as  one  calling  for  considerable  accommodative  adjust- 
ment. Then  the  previous  wearing  of  concave  lenses  is  perhaps 
partly  responsible  for  the  four  degrees  of  esophoria  complained 
of,  for  with  these  glasses  on  one  end  of  the  astigmatic  interval 
in  the  left  eye  calls  for  one  and  a  half-diopters  of  accommoda- 
tion which,  in  turn,  calls  for  two  and  a  quarter  degrees  of  con- 
vergence in  order  to  maintain  standard  co-ordination.  And  this 
for  one  eye  only. 

The  age  of  the  patient,  the  habit  of  excessive  convergence 
due  to  occupation,  also  the  habit  of  accommodation  aggravated 
by  the  occasional  use  of  glasses  calling  for  increased  ciliary 
effort,  are  all  factors  to  be  considered  by  an  examiner,  espe- 
cially if  his  patient  returns  in  a  day  or  two  and  complains  of  a 
"thin  fog,"  etc. 

The  temptation  to  advise  the  immediate  use  of  lenses  which 
the  optometrist  feels  sure  represent  the  full  correction  of  his 
patient's  ametropia  is  very  strong  indeed,  and  if  he  has  an 
intelligent  patient  to  reason  with  this  judgment  is  often  correct. 
But  if  his  patient  happens  to  be  of  the  timid  kind,  or  one  who 
thinks  the  acuity  of  vision  to  be  had  after  one  day's  use  of 
glasses  is  the  only  thing  to  judge  their  merits  by,  then  it  is 
wise  to  "make  tzvo  bites  of  a  cherry"  and  indulge  the  patient's 
own  notions  by  giving  a  temporary  correction  slightly  over  or 


ILLUSTRATIVE  CASES  1 37 

under  that  which  is  really  indicated,  and  which  will  eventually 
Iiave  to  be  given. 

It  is  cases  such  as  these  that  render  the  science  of  optometry 
inexact,  for  an  examiner  must  always  remember  that  attached 
to  every  pair  of  eyes  is  a  different  individual  with  a  different 
body,  a  different  occupation,  different  habits  and  different  ideas 
as  to  different  things,  and  so  each  patient  requires  different 
judgment  and  different  explanations  and  encouragements. 

And  it  is  for  these  differences  that  in  optometry,  as  in  other 
specialties,  "many  are  called  and  few  are  chosen." 


CHAPTER    IX. 

Multiple  Methods  in  Optometry  and  Their  Value  in 
■Corroborative  Measurements.  —  The  Systematic 
Keeping  of  Records  and  the  Importance  of  "Case 
History",  Including  Resourcefulness,  and  Mechani- 
cal Mydriasis. 

MULTIPLE  METHODS.  Eye-measuring  embraces 
many  "metrys"  and  the  able  optometrist  must  be  master  of  them 
all.  Even  in  the  method  to  which  the  name  static  skiametry 
has  been  logically  given  there  are  many  ways  of  applying  its 
optical  principles.  The  word  "static,"  as  is  well  known,  is  used 
to  designate  bodies  at  rest,  or  forces  in  equilibrium.  The 
medical  examiner  attempts  to  induce  this  rest  of  the  muscles, 
controlling  the  accommodation  of  an  eye,  by  instilling  into  the 
cul-de-sac  of  this  organ  some  one  of  a  series  of  powerful 
toxicants,  and  thus,  for  the  time  being,  practically  transform- 
ing a  living  eye  into  a  sort  of  schematic  one. 

Non-medical  examiners,  on  the  other  hand,  attempt  the 
relaxation  of  this  accommodation  by  having  their  patients  look 
toward  some  distant  object  in  order  to  thus  coax  the  muscles 
into  a  condition  of  inactivity,  and  in  further  explanation  it  may 
be  truthfully  said  that  in  many  cases  one  overdoes  the  matter 
while  the  other  underdoes  it.  The  medical  examiner's  over- 
doing consists  in  forcing  the  eye  into  an  abnormal  condition 
in  which  the  co-ordination  of  accommodation  and  convergence 
is  temporarily  destroyed,  this  destruction  depending  of  course 
upon  the  strength  of  the  drug  used,  and  the  duration  and  fre- 
quency of  its  instillation,  as  well  as  upon  the  idiosyncrasies  of 
the  patient.    The  results  obtained  by  measuring  the  refraction 


MULTfPLE  METHODS  1 39 

of  an  eye  while  it  is  in  a  state  of  what  might  be  called  "local 
intoxication"  would  seem  to  call  for  judgment  of  the  very- 
highest  type  in  order  to  make  the  theoretical  conform  to  the 
practical. 

Regarding  the  non-medical  examiner's  manner  of  using  the 
static  method,  especially  in  those  cases  where  the  muscle  action 
is  liable  to  be  particularly  vigorous,  it  can  be  likened  to  the 
old  story  of  the  blind  leading  the  blind,  for  the  reason  that  if  the 
patient  fails  to  maintain  the  requisite  muscular  relaxation  the 
examiner  has  no  means  of  knowing  what  action  has  really 
taken  place,  and  his  findings,  therefore,  are  likely  to  prove  very 
unreliable. 

Spasms  of  accommodation,  as  they  are  termed,  are  probably 
responsible  for  more  mistakes  being  made  in  the  non-toxic 
manner  of  employing  the  static  method  than  can  be  attributed 
to  the  carelessness  of  patients  in  looking,  or  in  trying  to  look, 
at  the  object  to  which  their  attention  has  been  directed. 

In  dealing  with  these  cases  there  are  two  ways  in  which 
static  skiametry  can  be  used.  One  consists  in  beginning  an 
examination  with  only  that  lens  before  the  patient's  eye  which 
is  necessary  to  produce  the  artificial  myopia  required  for  the 
operating  distance,  whatever  that  may  be,  and  then,  if  the  case 
is  a  hypermetropic  one,  the  convex  lenses  are  to  be  gradually 
increased  in  strength  until  the  reversal  point  of  the  shadow  is 
obtained. 

If  the  case  is  one  of  true  myopia,  however,  then  an  over- 
correction is  necessary,  and  the  concave  lenses  used  for  this 
purpose  are  to  be  gradually  decreased  in  strength  until  the 
reversal  point  of  the  shadow  is  found.  This  manner  of  increas- 
ing in  hypermetropia  and  of  decreasing  in  myopia  is  called  the 
amplifying  method. 

Overcorrecting  in  hyperopic  cases  and  undercorrecting  in 
myopic  ones  have  been  termed  the  fogging  method.  And  where 
ocular   skiametry    is    performed    in   a   non-toxic   manner    this 


140  MULTIPLE    METHODS 

method  of  decreasing  lens  values  in  hypermetropia  and  of  in- 
creasing them  in  myopia  will  often  prove  of  great  assistance  to 
an  examiner,  and  especially  so  if  applied  in  a  binocular  manner, 
for  then  the  co-ordinate  action  of  accommodation  and  conver- 
gence is  such  as  to  give  the  most  reliable  results.  This,  of  course, 
includes  more  particularly  those  cases  where  the  age  of  the 
patient  is  such  as  to  lead  an  examiner  to  fear  spasmodic  muscle 
action. 

In  cases  of  persons  fifty  years  of  age  or  older,  wherein 
presbyopia  has  a  tendency  to  overcome  spasm  of  accommoda- 
tion, then  static  skiametry  will  frequently  be  found  quite  trust- 
worthy, but  where  the  age  of  the  patient  is  less  than  fifty  years 
then  a  method  more  reliable  must  be  used  to  determine  true 
refractive  conditions. 

In  the  toxic  application  of  static  skiametry  it,  of  course, 
matters  little  whether  the  amplifying  or  fogging  method  is  used, 
for  here  the  accommodation  is  supposed  to  be  in  abeyance  and 
the  examiner  can  suit  his  own  convenience  in  regard  to  the 
manner  in  which  he  alters  his  lens  quantities.  But  the  toxic 
method  has  disadvantages  along  many  lines  when  it  is  viewed 
from  both  scientific  and  economic  standpoints.  In  its  scientific 
aspect  it  fails  entirely  to  tell  anything  about  muscle  tension  at 
the  reading  point,  leaving  this  to  be  estimated  and  guessed  at 
by  the  examiner,  while  this  reading  point,  as  is  well  known, 
constitutes  one  of  the  most  important  ends  for  which  glasses  are 
adapted.  Frequently,  too,  for  distance  purposes  a  medical 
examiner  is  led  to  advise  glasses  from  a  theoretical  instead  of  a 
practical  knowledge  of  the  true  conditions  present. 

All  cycloplegics,  as  pointed  out  before,  are  of  necessity 
mydriatics,  and  the  mydriasis  they  produce  constitutes  a  dis- 
turbing factor,  causing  the  pupillary  field  to  become  so  enlarged 
as  to  add  to  skiametric  complications  and  to  increase  the  diffi- 
culties of  the  method. 

Viewed  from  an  economic  standpoint  the  toxic  method  tends 


CORROBORATIVE   MEASUREMENTS  I4I 

toward  the  needless  distress  of  patients,  causes  a  quite  unneces- 
sary waste  of  valuable  time,  in  waiting  for  the  action  of  the 
cycloplegic,  and  takes  a  foolish  chance,  even  if  only  a  slight  one, 
of  risking  a  possibility  of  blindness  resulting  from  glaucoma. 

Every  working  distance  at  which  static  skiametry  is  prac- 
ticed, whether  by  toxic  or  non-toxic  means,  really  constitutes  a 
method  in  itself,  and  for  the  reason  that  the  nearer  a  patient's 
eye  an  examination  is  made  the  more  carefully  must  the  appear- 
ance of  the  shadow,  as  well  as  other  features  of  the  test,  be 
studied.  For  instance,  in  an  examination  made  at  eighty  inches 
a  half-diopter  convex  working  lens  quantity  would  have  to  be 
placed  before  the  patient's  eyes  in  order  to  produce  artificial 
myopia  and  focus  the  parallel  rays  of  light  emanating  from  the 
retina  of  an  emmetrope.  Here  the  behavior  of  the  shadow 
would  be  much  quicker,  while  its  color  and  intensity  would  be 
more  pronounced  than  if  the  test  were  made  at  forty  inches, 
where  a  one-diopter  convex  working  lens  was  used. 

A  test  made  at  forty  inches  might  also  prove  very  satis- 
factory, while  one  made  at  ten  inches,  using  a  four-diopter  lens, 
might  be  anything  but  satisfactory,  even  in  the  same  eye.  Thus 
it  will  be  seen  that  as  a  student  delves  deeper  into  the  intricacies 
of  skiametry  the  more  complicated  does  the  system  seem  and 
the  more  manifold  do  its  methods  appear. 

Experience,  however,  does  wonders  in  developing  skill  and 
judgment,  so  that  old  examiners,  as  well  as  students,  profit  by 
constant  every-day  work,  just  as  old  users  of  the  ophthalmoscope 
improve  by  daily  practice  with  this  valuable  little  instrument  for 
scanning  the  ocular  fundus.  The  truly  wise,  therefore,  will 
never  miss  an  opportunity  to  examine  a  case. 

CORROBORATIVE  MEASUREMENTS.  It  is  not  so 
very  long  ago  when  to  possess  an  optometer  of  simple  make,  or 
a  modest  trial  case,  seemed  to  be  all  that  an  examiner  needed 
in  order  to  cope  with  the  requirements  of  his  cases.    But,  thanks 


142  CORROBORATIVE   MEASUREMENTS 

to  the  progressives,  which  include  patients  as  well  as  examiners, 
that  time  has  gone  by  and  accuracy  and  attention  to  detail  are 
now  the  order  of  the  day  in  optometric  practice. 

To  do  high-class  work  at  the  present  time  (and  he  who  does 
not  do  it  is  pretty  sure  to  be  left  in  the  race),  an  optometrist 
must  be  thoroughly  familiar  with  the  various  methods  and 
devices  which  have  received  the  stamp  of  approval  of  those  of 
recognized  ability  in  this  field. 

At  first  thought,  it  would  seem  as  though  the  trial  case 
ought  to  be  given  primary  attention,  on  account  of  its  age,  but, 
logically,  it  should  come  last  because  it  offers  the  nearest 
approach  to  an  actual  pair  of  glasses,  and  because,  too,  it 
practically  gives  the  only  means  of  determining  binocular  vision 
with  any  degree  of  satisfaction. 

To  ocular  skiametry,  however,  belongs  the  first  place  in 
the  refractive  scale,  not  from  its  priority  of  discovery,  but 
rather  from  a  utilitarian  standpoint.  It  is  not  only  the  great 
pathfinder  that  points  the  way  for  other  work,  but  it  is  also  the 
great  verifier  that  tells  whether  the  other  work  is  correct  or  not. 
In  its  most  approved  application  it  discloses  minute  opacities 
of  the  cornea  and  crystalline  lens,  thereby  giving  information  at 
once  which  the  ophthalmoscope  could  not  locate  except,  possibly,- 
after  a  long  time-consuming  hunt. 

It  tells  of  the  presence  of  astigmia,  its  character  and  approxi- 
mate axis,  and  also  whether  it  is  complicated  with  any  error 
requiring  the  correction  of  spherical  lenses. 

It  shows  refractive  conditions  independent  of  the  patient's 
age,  language  or  answers,  and  serves  to  check  carelessness  in 
all  persons. 

In  children  it  is  of  invaluable  service,  and  in  those  whose 
hearing  is  faulty  it  saves  much  shouting  and  misunderstanding. 

Its  use,  therefore,  comes  at  both  the  beginning  of  an  exam- 
ination and  at  its  end,  and  if  astigmia  of  considerable  amount 


CORROBORATIVE   MEASUREMENTS  143 

is  disclosed  it  is  a  source  of  satisfaction,  though  perhaps  not 
absolutely  necessary,  to  use  a  keratometer  and  endeavor  to  ob- 
jectively locate  the  exact  axis  of  the  error.  Then  following 
these  methods  it  is  well  to  ascertain,  subjectively  of  course, 
whether  vision  is  in  harmony  with  refraction,  if  it  be  found 
otherwise  then  the  ophthalmoscope  should  be  employed  to  ascer- 
tain, if  possible,  why,  and  thus  enable  the  optometrist  to  know 
whether  the  case  is  one  calling  for  glasses,  for  medical  treat- 
ment, or  for  both. 

If  the  vision  and  the  refraction  agree  in  a  monocular  manner, 
but  not  in  a  binocular  one,  then  phorometric  devices  are  to  be 
called  into  requisition.  Thus  it  will  be  seen  that  in  the  order  of 
their  use  skiametry  is  first,  keratometry  second,  trial-case  lenses 
third,  and  then,  if  needed,  ophthalmoscopy  fourth,  phorometry 
fifth  and  perimetry  sixth. 

Three  of  these  methods  represent  the  objective,  and  three 
the  subjective,  so  that  practically  all  of  the  six  methods  are  inter- 
dependent, the  only  one  which  might  really  be  dispensed  with 
being  the  cornea  measure,  and  this  it  not  advisable. 

In  all-round  optometric  work  the  placing  of  sole  depend- 
ence upon  one  method,  one  device,  or  one  system,  for  success, 
is  about  as  foolish  as  it  would  be  to  place  like  dependence 
upon  one  method,  one  device,  or  one  system  in  the  practice  of 
any  other  professional  calling,  where  the  conditions  are  likely 
to  vary  in  different  cases. 

Then,  too,  the  use  of  examination  room  apparatus,  whose 
only  value  is  to  mystify  patients  and  make  them  believe  they 
are  undergoing  a  thorough  scientific  examination,  is  a  means 
hardly  calculated  to  maintain  that  lasting  public  confidence 
which  usually  contributes  to  a  long  and  increasing  practice. 
Nor  is  it  wise  to  idle  away  a  patient's  time  in  needless  visual 
tests  merely  for  the  purpose  of  trying  to  create  favorable 
impressions  regarding  professional  ability,  for  there  is  now 
enough  that  is  of  real  value  in  optometric  work  to  gain,  with 


144  SYSTEMATIC  CASE  RECORDS 

intelligent  use,  the  confidence  of  educated  as  well  as  unedu- 
cated patrons. 

To  attain  the  very  highest  order  of  practical  scientific 
results  should  be  the  well  defined  aim  of  those  who  devote 
either  all  or  part  of  their  time  and  ability  to  the  mastery  of 
physiologic  optics.  And  as  a  means  to  this  end  the  practice 
of  systematically  corroborating  all  ocular  measurements  will 
be  found  to  act  as  a  preventive  to  the  making  of  those  mis- 
takes which,  when  discovered  by  some  other  examiner,  are  so 
difficult  of  explanation. 

SYSTEMATIC  CASE  RECORDS.  As  one  of  the  pro- 
nounced aids  to  successful  examination  room  work,  a  brief 
reference  will  here  be  made  to  systematic  examinations  and  the 
practical  assistance  to  be  derived  from  carefully  recording 
them. 

The  great  value  of  this  troublesome  detail  can  not  be  em- 
phasized too  frequently  for,  as  has  been  remarked  before,  ocu- 
lar skiametry  is  the  great  refractive  pathfinder,  and  tlierefore 
when  the  path  has  once  been  found  it  is  wise  to  keep  it,  and 
keep  track  of  its  various  windings. 

A  blank  form  should  be  used  containing  properly  named 
spaces  wherein  entries  can  be  systematically  made,  so  that 
nothing  of  importance  may  be  overlooked  in  the  hurry  of  busy 
days.  This  blank  should  be  large  enough  to  contain  on  one 
sheet  a  complete  record  of  everything  pertaining  to  a  case. 

This  is  an  age  of  card  indexes,  and  the  makers  of  these 
valuable  time-savers  seem,  at  last,  to  appreciate  the  needs  of 
those  who  are  engaged  in  optometric  work,  for  they  now  make 
their  cards  large  enough  to  meet  the  optometrist's  purposes, 
as  shown  by  Fig.  58. 

This  card  is  five  inches  wide  by  eight  inches  long,  and  is 
plain  on  the  back  so  as  to  permit  of  space  for  entries  covering 
repairing  and  changes.     It  is  designed  in  such  a  manner  as  to 


systematic  case  records 
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AUTHOR  S  RECORD  BLANK. 


146  SYSTEMATIC  CASE  RECORDS 

expedite  examinations  and  to  show  at  a  glance  whether  con- 
ditions are  usual  or  unusual.  The  space  for  case  history  while 
not  large  will  be  found  ample  when  taken  in  connection  with 
the  preliminary  findings. 

Generally  speaking,  "case  history"  covers  only  the  symp- 
toms complained  of  by  the  patient  but,  broadly,  all  findings 
that  serve  as  an  aid  to  the  formation  of  correct  judgment 
constitute  optometric  case  history  in  its  true  sense. 

The  records,  both  old  and  new,  which  are  made  use  of 
during  the  week  also  serve  as  a  kind  of  day-book  and  thus  in 
the  end  really  save  more  labor,  from  a  bookkeeping  stand- 
point, than  their  use  entails. 

To  describe  more  completely  the  uses  for  which  a  record 
blank  is  intended  it  can  be  stated  that  the  age  of  the  patient 
may  be  marked  in  cipher,  so  that  inquisitive  persons  cannot 
gratify  idle  curiosity  if  the  record  happens  to  be  left  care- 
lessly exposed. 

The  examination  covers  "occupation,"  for  it  is  important 
to  know  what  kind  of  work  the  eyes  are  to  be  used  for.  Then 
follows  the  use  of  the  ophthalmoscope  and  a  cursory  inspection 
of  the  lids,  cornea,  iris,  lens  and  fundus.  As  the  word  opto- 
metric pertains  to  eye  measuring  in  general  it  will  be  seen  that 
eye  measuring  in  detail  ought,  logically,  to  have  its  word 
terminals  in  metrics  too,  hence  this  rule  has  been  followed  as 
far  as  possible  in  the  make-up  of  this  blank. 

Skiametric  covers  both  static  and  dynamic  methods,  space 
being  given  for  one-third,  one  and  six-millimeter  data.  Ke- 
ratoma ric  gives  the  corneal  mal-curvatures  and  axes. 

Phacometric  covers  the  subjective  findings  made  with  trial- 
case  lenses.  While  "U.  V."  stands  for  uncorrected  vision,  and 
"C.  V."  for  corrected.  "Amp"  for  "amplimetric"  is  the  same 
as  amplitude  of  accommodation,  only  shorter.  If  it  is  desired 
to  have  the  blank  embrace  further  tests,  then  the  word  peri- 
metric could  be  used  to  cover  the  use  of  the  perimeter,  and 


SYSTEMATIC  CASE  RECORDS  I47 

under  prismometric  could  be  recorded  the  tendencies  toward 
deviation  of  the  extrinsic  muscles,  called  phorometric,  while 
under  a  classification  of  "tropometric"  could  be  shown  the 
actual  deviations.  Kratomctric  pertains  to  strength,  and  so 
would  show  duction  tests  and  exercises,  all  of  which  could  be 
expressed  in  degrees  with  the  exception  of  the  exercises,  and 
the  word  "over"  could  call  attention  to  them  on  the  back  of  the 
blank  where  space  is  ample. 

Presbymetric  or,  literally,  old-man  measuring,  is  the  same 
as  presbyopic,  or  old-man  vision.  The  prefix  ocular,  of  course, 
connects  the  eye  with  all  of  these  measurements. 

"Previous  formula"  and  the  rest  of  the  blank  needs  no 
translation,  unless  it  is  to  call  attention  to  "segs"  for  segments, 
in  bi-focal  work,  and  to  add  that  under  "lenses"  can  be  noted 
the  regular,  toric,  tinted  and  fused  kinds.  First  quality  lenses 
could  be  termed  cent  ex,  and  second  quality  could  be  desig- 
nated as  ordigrad. 

For  purposes  of  explanation,  let  it  be  supposed  that  an 
examiner  is  fallible  and  does  err  in  judgment,  and  that  a  patient 
returns  and  has  a  slight  change  made.  This  is  duly  recorded 
on  the  back  of  the  blank  as  well  as  the  fact  that  no  charge  was 
made  for  this  change. 

In  the  course  of  a  few  months,  perhaps,  a  new  "O.  D."  is 
supplied,  which,  with  its  price,  is  also  recorded,  and  thus  the 
blank  will  last  for  years,  for  whenever  the  patient  calls  the 
blank  can  be  taken  into  the  examination  room  and  made  to 
serve  as  a  complete  "book  of  the  play." 

When  skiametric  examinations  are  recorded  they  seldom 
have  to  be  repeated  in  return  cases.  It  is  only  the  subjective 
tests,  and  the  variations  of  judgment  that,  ordinarily,  require 
attention. 

Therefore  when  it  is  stated  that  systematic  ocular  examina- 
tion records  are  very  valuable,  from  a  practical  standpoint,  this 
statement  might  go  further  and  class  them  along  with  examina- 


148  RESOURCEFULNESS 

tion  rooms  and  claim  both  as  absolutely  essential  in  this  day 
and  age,  when  a  pronounced  success  in  optometry  is  only 
achieved  by  paying  strict  attention  to  every  detail  of  method, 
place  and  device. 

RESOURCEFULNESS.  When  to  rely  on  a  patient's 
"Yes"  or  "No,"  and  when  not  to,  requires  no  small  amount 
of  knowledge  of  human  nature,  as  well  as  ability  as  a  cross- 
questioner.  Of  course  ocular  skiametry  and  other  objective 
means  place  an  examiner  in  a  position  largely  independent  of 
a  patient's  answers  or  intelligence,  yet  it  is  always  a  source  of 
satisfaction  to  have  one  method  corroborate  another,  since  there 
are  many  ways  in  which  to  be  wrong  and  only  one  way  in 
which  to  be  exactly  right.  With  so-called  regular  conditions 
skiametrists  are  likely  to  have  little  trouble,  but  the  irregular 
kind  frequently  call  for  considerable  versatility  on  the  part  of 
an  examiner  in  order  to  extricate  himself  from  a  refractive 
corner,  so  to  speak. 

To  illustrate  this,  a  case  of  nystagmus  once  presented  itself 
which  had  been  seen  by  a  half-dozen  able  speciahsts.  The  age 
of  the  patient  was  twenty  years,  and  the  glasses  in  use  were 
one-diopter  concave  sphericals  for  both  eyes,  which  gave  an 
acuity  of  vision  equal  to  about  ten  two-hundredths. 

The  use  of  the  skiascope  showed  the  presence  of  myopic 
astigmia,  zvith  the  rule,  but  the  spasmodic  action  of  the  muscles 
precluded  the  ascertaining  of  the  amount.  By  recourse  to  the 
keratometer  and  by  engaging  the  patient  in  a  long  conversa- 
tion regarding  daily  work,  in  order  to  quiet  the  spasm,  it  be- 
came possible  to  locate  a  corneal  mal-curvature  of  about  five 
diopters.  The  use  of  the  mirror  again  showed  the  absence  of 
any  error  at  right  angles,  and  glasses  of  four  diopters  concave 
cylindric  at  axis  180  after  thirty  days'  use  increased  vision  to 
a  little  better  than  twenty  one-hundredths. 

When  it  is  borne  in  mind  that  this  case  had  been  under  care- 


MECHANICAL   MYDRIASIS  I49 

ful  observation  for  twelve  years,  and  that  no  expense  had  been 
spared  in  consulting  the  most  eminent  specialists,  the  joy  of 
the  patient  over  the  results  achieved  can  readily  be  imagined. 

A  haphazard  trial  of  test  lenses  might  have  resulted  in  a 
clue  which  could  have  been  followed  up  satisfactorily,  perhaps, 
but  this  less  certain  method  frequently  leads  an  examiner 
astray  through  the  patient's  failure  to  appreciate  and  give  an 
encouraging  answer  to  a  partial  correction. 

In  the  refractive  examination  of  the  eyes  of  children,  deaf 
persons,  mutes  and  illiterates,  ocular  skiametry  offers  about  the 
only  reliable  means  for  independently  determining  the  kind  and 
strength  of  proper  glasses. 

In  this  same  category  might  be  included  those  persons  who 
are  only  partially  deaf,  and  who  fail  to  respond  to  all  questions 
asked  them.  Also  those  persons  who  do  not  speak  the  same 
language  the  examiner  does,  and  careless  persons  who  some- 
times prefer  to  joke  and  thus  unconsciously  cause  an  examiner 
to  become  careless  himself.  Then  there  are  the  ultra  careful 
persons  whose  answers  are  about  as  misleading  as  though  they 
too  were  careless. 

All  of  these  and  many  others  tend  to  show  the  value  of 
ocular  skiametry,  for  success  must  be  achieved,  no  matter  what 
the  obstacles  are,  as  an  examiner  can  ill  afford  to  endanger  his 
reputation  through  poor  work. 

MECHANICAL  MYDRIASIS.  As  pointed  out  by  other 
writers,  the  production  of  mydriasis  by  temporary  paralysis 
serves  to  uncover  corneal  zones  which  add  much  to  the  con- 
fusion of  an  operator  in  making  his  measurements  by  the 
shadow  test,  owing  to  the  refractive  variations  found  from 
center  of  cornea  to  circumference  of  pupil. 

Then,  too,  habits,  which  are  formed  through  the  efforts 
of  nature  in  trying  to  adapt  herself  to  the  best  conditions  pos- 
sible,  are  no   doubt   responsible   for  the  difference   in   size  of 


150  MECHANICAL  MYDRIASIS 

ocular  pupils  where  the  ages  and  refractive  errors  of  patients 
are  the  same.  Skiametrists  will  therefore  find  that  mydriasis 
produced  by  magnifying  will  give  them  better  results  than 
where  the  constricting  muscles  of  the  pupil  are  paralyzed  by 
toxicants,  and  the  reason  for  this  lies  in  the  fact  that  through 
magnification  only  that  portion  of  the  cornea  which  is  limited  to 
the  size  of  the  pupil  is  measured,  thus  avoiding  the  peripheral 
zones. 

Enlargement  by  magnification  would  seemingly  mean  an 
increase  in  size  at  the  expense  of  definition.  Let  it  be  con- 
sidered, then,  whether  this  is  really  so  or  not.  The  word 
"definition,"  as  used  in  optics,  means  the  power  of  a  lens  to 
give  an  image  of  anything,  or  part,  so  as  to  clearly  distinguish 
it  from  its  surroundings.  But  this  is  perhaps  misleading,  as 
experienced  microscopists  say  that  a  lens  of  low  power  often 
works  better  than  one  of  high  power,  because  with  a  low- 
power  lens  a  better  general  idea  may  be  had  of  the  object,  even 
at  the  expense  of  size,  than  if  it  were  viewed  through  a  high- 
power  lens. 

It  might  be  reasoned  from  this,  therefore,  that  it  applied  to 
the  magnifying  of  the  retinal  shadow.  But  here  comes  the 
examiner's  own  vision  and  the  law  of  a  five-minute  angle  gov- 
erning its  acuity.  If  he  operated  at  a  much  nearer  point  than 
forty  inches,  any  increase  in  size  of  shadow,  without  correspond- 
ing increase  in  substance  of  which  it  is  composed,  might 
interfere  with  the  sharpness  of  demarcation  caused  by 
magnifying.  But  many  ocular  pupils  are  so  small  that  the 
retinal  shadow  gives  a  visual  angle  of  less  than  one-half,  per- 
haps, of  what  it  should  at  forty  inches  away,  and  so,  when  the 
pupil  is  magnified  to  several  times  its  original  size,  the  increase 
in  visual  angle  more  than  compensates  for  the  decrease  in 
sharpness  of  outline.  Hence  this  explanation  to  theoretically 
account  for  that  which  those  who  use  this  method  learn  to  be 
a  fact  from  actual  experience. 


MECHANICAL  MYDRIASIS  I5I 

A  simple  experiment  can  be  tried  which  will  serve  to 
emphasize  the  superiority  of  this  magnification  principle.  If 
a  patient  will  hold  a  convex  seven-diopter  spherical  lens  two 
inches  in  front  of  his  eye  and  let  an  examiner  compare  the 
sharpness  of  outline  of  the  union  between  the  iris  and  the 
sclerotic  from  a  distance  of  forty  inches  away,  and  then  deter- 
mine which  one  of  the  patient's  two  eyes  is  the  easiest  to  see, 
the  magnified  or  the  unmagnified  one,  the  difference  will  be 
very  apparent,  and  the  larger  iris  will  seem  to  lose  little  if  any 
of  its  color  or  intensity  on  account  of  magnification.     Figs. 

Fig.  59.  Fig.  6o. 


REGULAR  SIZE  PUPIL.  AREA  OF  MAGNIFIED  PUPIL. 

59  and  60  illustrate  the  relative  size  between  an  average  pupil 
and  one  enlarged  three  diameters. 

The  working  distance  at  which  an  examiner  operates  will, 
of  course,  affect  the  magnifying  power  of  whatever  lenses  may 
be  used,  but  as  a  rule  this  magnifying  principle  will  be  seen  to 
take  care  of  itself,  for  in  high  degrees  of  hypcrmetropia,  where 
small  pupils  are  apt  to  be  found,  the  enlargement  caused  by 
the  lenses  in  an  instrument  constructed  on  mobile  principles 
will  usually  be  ample  for  all  practical  purposes. 

Where  an  instrument  is  not  available,  a  three-cell  trial 
frame  can  sometimes  be  used  to  advantage,  especially  when  the 
first  and  third  cells  are  widely  separated.     In  this  case  place 


152  MECHANICAL  M\T)RIASIS 

a  minus  20.  D.  spheric  lens  in  the  cell  next  to  the  patient,  and 
a  plus  16.  D.  spheric  lens  in  the  cell  next  to  the  examiner,  the 
plus  16,  D.  lens  acting  as  an  appreciable  magnifier,  and  its 
distance  from  the  minus  20.  D.  lens  will  be  sufficient  to  neu- 
tralize the  4.  D.  difference  in  the  strength  of  the  lenses.  In  this 
way  small  pupils  can  often  be  doubled  in  area,  which  helps 
greatly  when  other  conditions  are  poor. 

Another  way  is  to  use  a  strong  concave  spheric  in  a  regular 
trial  frame  and  then  hold  a  weak  convex  lens  much  farther 
away.  The  manner  being  the  same  as  the  strong  convex  lens 
is  held  in  practising  indirect  ophthalmoscopy. 


CHAPTER  X. 

Value  of  Instruments  in  Practising  Optometry. — 
Mobile  and  Unit  Lens  Systems. — Various  Instru- 
ments Used  in  Skiametry^  With  Descriptions  of 
Their  Mechanical  Construction. 

VALUE  OF  INSTRUMENTS.  The  value  of  instruments 
in  optometric  practice  can  hardly  be  overestimated,  if  accu- 
racy, encouragement  and  speed  are  to  be  considered.  For  while 
it  is  true  that  all  optometrists  should  be  so  trained  as  to  be 
able  to  do  their  work  with  crude  apparatus,  it  is  also  true  that 
they  should  be  educated  in  the  expert  handling  of  devices  which 
tend  to  make  their  work  more  efficient. 

All  optometric  instruments  are  at  best  only  tools  which 
depend  for  their  usefulness  upon  the  intelligence  of  those  who 
handle  them.  The  confession,  therefore,  of  inability  to  use 
an  instrument  is  tantamount  to  a  confession  of  incompetency. 
Some  tools  and  instruments  have  greater  scientific  and  economic 
value  than  others  have,  and  it  frequently  happens  that  the 
instrument  or  device  whose  manipulation  is  easiest  to  acquire 
is  not  always  the  best  one  to  use.  The  inexperienced  should 
be  influenced  by  the  experienced  in  the  selection  of  their  exam- 
ination room  armament,  provided  this  experience  is  adequate 
and  its  possessor  does  not  belong  to  that  class  of  examiners 
who  get  into  ruts  and  are  incapable  of  extricating  themselves, 
no  matter  what  the  true  value  of  the  optometric  inducement 
may  be. 

In  the  selection  of  instruments  there  is  one  point  which 
usually  commends  itself  to  those  who  have  had  opportunities 
of  using  various  kinds,  and  that  is  the  superiority  of  mobile 


154 


MOBILE    LENS    ACTION 


action  over  the  unit  action  of  lenses.  This  so-called  "unit" 
in  the  ophthalmic  lenses  in  general  use  to-day  is  termed  "one 
diopter,"  but  in  reality  the  unit  comes  nearer  to  being  an  eighth 
of  a  diopter,  as  lenses  are  now  employed,  these  small  quan- 
tities acting  as  steps  whereby  the  accommodation  of  an  eye  is 
compelled  to  jump  from  one  adjustment  to  another. 

To  overcome  this  jumping  principle  in  the  measuring  of 
convergence  the  "Risley"  mobile  prism  was  invented.  This 
prism  arrangement  serves  to  change  these  abrupt  degree-jumps 
into  a  sort  of  sliding  motion,  thereby  permitting  a  gradual  in- 
crease or  decrease  in  the  light  deviation,  and  resembling  the 
action  of  a  wedge  while  being  made  to  lift  a  weight. 


Fig.  6i 


^4D 


^/mM 


REFRACTION  BY  LENSES  PLACED  CLOSE  TOGETHER. 


MOBILE  LENS  ACTION.  With  both  cylindric  and 
spheric  lenses  this  sliding  principle  can  be  imitated.  Thus  two 
convex  lenses  of  four  diopters  each  when  placed  close  together 
on  their  optical  axes  give  a  combined  refraction  of  eight  diop- 
ters, with  a  focal  power  equal  to  five  inches.  Separate  these 
two  lenses  two  inches  and  their  combined  action  will  represent 
nine  diopters  of  refraction,  having  a  focal  distance  of  four  and 
a  half  inches.  The  increasing  or  decreasing  of  the  distance 
between  any  series  of  lenses  on  their  optical  axes  serves  to 
produce  a  mobile  efifect  similar  to  the  action  of  the  crystalline 
lens  in  a  living  eye,  thus  enabling  accommodation  to  be  given 


MOBILE    LENS    ACTION 


155 


the  same  character  of  assistance  as  that  accorded  to  convergence 
by  a  mobile  prism.  Figs.  6i  and  62  will  make  this  point  plainer. 
That  this  mobile  action  is  a  valuable  factor  in  dealing  with 
stubborn  cases  of  spasm  is  not  difficult  to  perceive,  any  more 
than  it  is  difficult  to  note  the  fact  that  the  raising  or  lowering 
of  a  heavy  safe  by  sliding  on  a  plane  is  easier  than  it  would 
be  by  using  a  series  of  steps.  The  evenness  of  the  sliding  mo- 
tion serves  to  induce  an  accuracy  of  action  that  can  hardly  be 
imitated  by  a  motion  which  might,  perhaps,  be  best  described 
as  by  jumps  or  by  leaps. 


Fig.  62. 


^'/i/nefi  foeuc. 


MD 


^4D 
REFRACTION   BY   LENSES    WHEN    SEPARATED. 


An  eye  is  often  considered  as  having  an  error  equal  to  one 
and  three-quarters  diopters,  whereas,  the  true  error  may  really 
be  one  and  five-eighths  diopters  or  one  and  seven-eighths,  the 
one  and  three-quarters  merely  indicating  an  approximate  cor- 
rection. In  many  cases  this  would  undoubtedly  be  near  enough, 
but  in  others  a  knowledge  of  the  exact  refraction  is  often  of 
importance.  Therefore,  where  a  mobile  lens  system  is  employed 
there  is  a  greater  tendency  toward  precision  than  where  lens 
units  are  relied  upon. 

Then  too,  the  relaxation  of  accommodation  will  be  found 
much  easier  with  a  mobile  lens  system  than  it  will  be  with  a 
unit  system,   for  in  reality  the  mobile  practically  amounts  to 


156 


UNIT  LENS  ACTION 


the  measuring  of  a  living  eye  by  means  of  an  artificial  one 
possessing  similar  refractive  powers  of  adjustment. 

The  invention  of  a  single  mobile  lens  capable  of  adaptation 
to  the  needs  of  mankind  would  undoubtedly  prove  a  great  boon, 
but  until  such  an  invention  appears  reliance  will  have  to  be 
placed  upon  a  series  of  lenses  arranged  for  the  accomplishment 
of  similar  purposes. 

Fig.  63. 


KING  S  BINOCULAR   HAND  TRIAL   SET. 


UNIT  LENS  ACTION.  There  is  one  form  of  the  step- 
like arrangement  of  lenses  that  will  be  found  exceedingly 
valuable  in  corroborative  work,  and  that  is  in  the  old-fashioned 
metal  or  hard  rubber  device  illustrated  by  Fig.  63. 


VARIOUS  INSTRUMENTS  USED   IN    SKIAMETRY  157 

There  should  be  four  pairs  of  plus  and  minus,  half  and  quar- 
ter-diopter spheric  lenses  mounted  so  they  can  be  used  in  either 
a  monocular  or  binocular  manner.  This  device  can  be  employed 
both  objectively  and  subjectively,  either  for  near  or  distant  tests, 
and  can  be  held  by  the  examiner  or  by  the  patient.  Its  con- 
venience in  the  addition  or  removal  of  weak  lens  power  serves 
to  determine  accommodative  action,  and  frequently  gives  that 
slight  fog  to  vision  which  enables  both  patient  and  examiner  to 
easily  differentiate  small  quantities  of  astigmia. 

In  the  final  study  of  a  case,  after  the  correcting  lenses  are  in 
position,  an  examiner  will  find  the  use  of  lenses  mounted  in 
pairs,  such  as  shown  in  Fig.  63,  and  placed  in  front  of  the  trial 
frame,  to  be  an  easy  way  of  obtaining  those  little  niceties  in 
refractive  adjustment  which  contribute  so  much  toward  the  com- 
plete visual  comfort  and  satisfaction  of  a  patient,  and  which  also 
make  one  examiner's  work  just  a  little  better  than  another's. 

VARIOUS  INSTRUMENTS  USED  IN  SKIAMETRY. 
Skiametry  is  somewhat  similar  to  indirect  ophthalmoscopy,  inas- 
much as  an  operator  is  obliged  to  do  several  things  at  one  time. 
After  shadow  testing  had  been  improved  and  brought  to  a  state 
approaching  practical  usefulness  by  men  like  Cuignet,  Parent, 
and  others,  it  was  found  that  its  application  entailed  such  fre- 
quent changing  of  lenses  as  to  discourage  its  common  use. 

The  first  effort  of  importance  along  the  line  of  labor-saving 
devices  for  skiametric  work  was  the  lens  rack,  or  hand  ski- 
ameter, to  which  the  name  of  Wiirdemann  is  frequently  at- 
tached, although  its  invention  is  claimed  by  a  large  number  of 
others. 

Fig.  64  illustrates  the  constructive  principle  of  this  instru- 
ment and,  as  will  be  seen,  it  consists  of  a  series  of  plus  and 
minus  spheric  lenses  mounted  in  such  a  manner  as  to  permit  of 
the  patient  holding  them  before  his  eyes  and  moving  the  lenses 
from  one  strength  to  another,  at  the  request  of  the  examiner. 


158 


VARIOUS  INSTRUMENTS  USED   IN   SKIAMETRY 


Inasmuch  as  it  proves  a  saving  of  time  and  labor,  this  device 
is  a  decided  improvement  over  the  use  of  single  lenses  placed 
in  a  trial  frame.  Among  the  drawbacks  to  its  use,  however,  will 
be  found  the  stupidity  and  carelessness  of  patients,  who  fre- 
quently permit  the  lenses  to  rest  at  angles  which  interfere  with 
their  correct  refraction  and  thus  necessitate  a  constant  readjust- 
ment of  the  rack  by  the  examiner.  Then,  too,  owing  to  this 
same  stupidity  and  carelessness,  a  patient  will  often  allow  the 
lenses  to  come  in  contact  with  the  skin  on  the  forehead,  eyelids 
or  cheeks,  and  thereby  soil  the  lenses  so  they  become  unfit  for 
use  until  after  they  have  been  cleaned. 

Fig.  64. 


SKIAMETRIC    LENS    RACK    OF    WURDEMANN. 


Quite  a  number  of  modifications  of  the  Wiirdemann  prin- 
ciple have  been  produced,  but  the  drawbacks  just  mentioned 
seem  common  to  them  all. 

The  Grain  disc  and  the  Standart  annular  ring  of  lenses  are 
both  popular:  the  first  named  being  on  a  stand  for  use  on  a 
table,  while  the  last  named  is  held  by  a  wall  bracket.  Fig,  65 
shows  the  large  disc  of  lenses  used  in  the  Grain  device. 

The  lenses  of  the  disc  can  be  either  spheric  or  cylindric  as  the 
examiner  chooses.  The  disc  can  also  be  revolved  by  the  exam- 
iner or  by  the  patient  at  the  former's  request.  These  discs,  or 
batteries  of  lenses,  are  something  of  an  improvement  on  the 
hand  rack  of  Wiirdemann,  inasmuch  as  they  hold  the  lenses  in 
such  a  position  as  to  permit  of  no  material  twisting  or  dis- 
turbance to  their  principal  axes.    The  reliance  on  the  patient  to 


VARIOUS  INSTRUMENTS  USED  IN   SKIAMETRY 


159 


turn  the  discs  and  the  necessity  for  troublesome  adjustments  as 
to  height,  together  with  the  annoyances  incident  to  keeping  the 
head  of  the  patient  so  situated  that  the  eyes  will  always  be  in 
proper  position,  constitute  some  of  the  reasons  why  these  de- 
vices have  not  been  in  greater  demand. 

The  Standart  "Umhramcter"  is  an  instrument  thoroughly 
vouched  for  by  its  inventor,  who  is  one  of  the  foremost  optom- 
etrists of  America;  Fig.  66  shows  its  general  construction. 

Fig.  65. 


LENS  DISC  USED  BY  GRAIN  AND  OTHERS. 


The  makers  of  this  device  tell  of  its  merits  in  the  following 
words : 

"Time  is  a  great  element  with  a  busy  refractionist.  A  pa- 
tient in  the  chair  and  a  half  dozen  waiting  means  that  unless 
the  operator  is  rapid  in  his  work,  some  of  the  waiting  ones 
will  get  tired  and  go  out. 

"The  Standart  Umbrameter  is  designed  to  save  time,  to 
contribute  to  accuracy  in  results  and  impress  the  client  with  the 
skill  and  efficient  equipment  of  the  up-to-date  refractionist. 


i6o 


VARIOUS  INSTRUMENTS  USED   IN   SKIAMETRY 


"Combining  accurately  all  spheres  from  one-quarter  to  six 
and  one-half  dioptrics  by  quarters,  and  from  six  and  one-half 
to  nine  dioptrics  by  halves,  and  all  cylinders  from  one-quarter 
dioptric  to  seven  and  three-quarters  dioptric  by  quarter  diop- 
trics, set  at  any  axis,  with  their  manipulation  easily  accom- 
pHshed  at  one  meter  distant,  makes  this  instrument  the  most 
perfect  adjunct  of  the  retinoscope  ever  devised. 

Fig.  66. 


STANDART  S    UMBRAMETER. 


"A  little  practice  will  make  it  an  indispensable  addition  to 
the  instrument ariiim  of  the  operating  room.  It  will  save  its 
cost  in  a  short  time  by  increasing  sales  during  the  busy  hours 
of  the  day,  rendering  changes  less  liable  to  be  necessary  and 
saving  that  valuable  element — time. 

"The  operation  is  simple:  Loosen  the  thumb  screws  on  rod 
pinions  and  grasp  the  hanging  upright  bar  with  the  right 
hand,  then  with  the  left  hand  turn  geared  lens  ring  around 
until  o  is  shown  in  the  number  aperture  on  lower  part  of  the 
frame ;  this  is  the  zero  point. 


VARIOUS    INSTRUMENTS    USED    IN    SKIAMETRY  l6l 

"Direct  the  patient  to  assume  an  easy  position  and  to  look 
towards  some  object  15  or  20  feet  away  pinned  upon  the  wall 
so  that  the  line  of  patient's  vision  will  just  come  over  the  top 
of  operator's  head  while  seated  40  inches  away  facing  patient. 

"Adjust  the  instrument  up  or  down,  turning  it  sideways  and 
tipping  the  annular  rings  up  or  down  to  bring  it  to  the  proper 
position  before  the  patient's  eye. 

"From  the  trial  set  slip  under  springs  on  the  back  of  the 
eye  hole  a  spherical  convex  lens  of  sufficient  power  to  create 
a  positive  pseudo  myopia.  If  the  case  is  one  of  known  myopia 
of  over  1. 00  D.,  leave  the  supplemental  lens  out,  or  if  it  is 
discovered  after  a  little  examination  that  it  is  a  case  of  true 
myopia  or  myopic  astigmatism,  then  this  supplemental  lens  may 
be  removed,  if  desired, 

"This  is  the  fogging  system  applied  to  skiascopy,  the  most 
accurate  yet  discovered.  There  is  a  diversity  of  opinion  as  to 
the  relative  value  of  piano  or  concave  mirrors.  We  suggest  for 
use  the  concave  of  about  i  dioptric  curve  and  with  a  hole  not 
more  than  two  millimeters  in  diameter. 

"Seated  on  a  revolving  stool  that  may  be  raised  or  lowered 
one  meter  (40  inches),  from  patient,  the  length  of  the  rods, 
and  a  light,  preferably  an  Argand  burner  with  a  flame  about  i 
to  lyz  inches  high,  over  the  head  of  the  patient  and  slightly 
back,  direct  the  patient  to  look  over  the  top  of  your  head  at 
some  object  on  the  wall. 

"In  the  right  hand  is  held  the  mirror  and  in  the  left  one  of 
the  rod  handles,  the  other  rod  being  suspended  therefrom  by 
an  S  link.  Secure  a  clear  fundus  reflex  through  the  aperture 
provided  for  the  patient  to  look  through,  and  then  turn  spheres 
until  one  medium  stands  still.  If  there  is  then  astigmatism 
present,  calculate  the  axis,  then  adjust  the  annular  ring  con- 
taining cylinders  so  that  the  mark  on  scale  shows  the  meridian 
determined  and  then  proceed  as  before  until  that  meridian  is 
neutralized.     Should  the  astigmatism  appear  in  the  vertical,  or 


1 62 


VARIOUS    INSTRUMENTS    USED    IN    SKIAMETRY 


its  approximations,  use  the  white  scale  revolving  the  lenses 
downward  bringing  the  cyls,  setting  vertically  on  the  instrument, 
downward.  Should  the  astigmatism  appear  in  the  horizontal, 
or  its  approximations,  then  use  the  red  scale  revolving  lenses 
set  in  the  instrument  horizontally  upward  into  position. 

Fig.  67. 


THE    MERIDEN    OCULOMETROSCOPE. 


"The  ring  containing  spheres  may  be  turned  down  or  up 
on  its  axis  to  suit  convenience  and  comfort  of  the  patient  with- 
out affecting  the  axis  of  the  cylinders." 

The  "Oculometroscope,"  made  by  the  Meriden  Optical  Man- 
ufacturing Company,  is  shown  in  Fig.  67. 

This  is  perhaps  the  latest  form  of  disc  instruments.  It 
carries  its  own  lamp  and  has  a  turning  rod  attached  to  each 
disc  whereby  an  examiner  is  enabled  to  change  lenses  without 


VARIOUS    INSTRUMENTS    USED    IN    SKIAMETRY  163 

altering  his  position  when  operating  at  a  distance  of  forty  or 
more  inches  away. 

The  manufacturers  of  this  instrument  set  forth  its  use, 
as  follows : 

"With  this  instrument  you  can  measure  the  far  point,  near 
point,  amplitude  of  accommodation,  hypermetropia,  myopia, 
presbyopia  and  astigmatism.  Also  the  muscular  insufficiencies 
by  using  a  prism  from  your  trial  case.  It  can  be  used  for 
both  objective  and  subjective  tests. 

"The  Oculometroscope  is  a  great  time  saver  in  using  the 
fogging  system,  and  in  retinoscopy  by  the  static,  dynamic  or 
fogging  methods.  With  it  you  can  locate  the  axis  for  cylin- 
ders without  the  use  of  a  chart. 

"As  a  time  saver  in  retinoscopy  this  instrument  is  unex- 
celled. You  can  save  the  time  usually  lost  in  changing  lenses 
in  trial  frame  and  in  finding  the  reflexes,  time  after  time,  and 
also  avoid  the  danger  of  small  errors  from  not  getting  the  one 
meter  distance  every  time, 

"Seat  the  patient  comfortably  before  the  instrument  with 
chin  in  the  rest  and  eyes  looking  through  the  open  disc.  Care 
must  be  taken  to  have  the  centers  of  the  discs  properly  ad- 
justed for  the  patient's  p.  d.  Have  the  patient  look  into  the 
distance,  relaxing  the  eye  as  much  as  possible.  Rotate  the 
lens  discs  by  rod  until  plus  i.oo  appears  in  the  indicators. 

"Turn  on  the  light,  and  with  the  plane  mirror  at  the  end  of 
the  graduated  rod  (which  is  exactly  one  metre  from  the 
patient's  eyes)  proceed  to  examine  the  eyes  with  the  mirror. 
You  do  not  have  to  move  mirror  from  position  to  change 
lenses  in  front  of  patient's  eyes,  and  you  are  always  sure  of 
maintaining  a  one-metre  distance. 

"This  means  a  great  saving  of  time  usually  lost  in  changing 
lenses  in  trial  frame,  and  finding  reflex,  time  after  time,  also 
lessens  the  danger  of  small  errors  from  not  getting  the  one- 
metre  distance  every  time." 


164 


VARIOUS    INSTRUMENTS   USED   IN    SKfAMETRY 


The  latest  model  of  what  is  known  as  the  "Geneva  Retino- 
scope,"  manufactured  by  the  Geneva  Optical  Co.,  of  Chicago, 
is  shown  in  Fig.  68. 

Fig.  68. 


THE  "geneva"  RETINOSCOPE. 


The  makers  put  forth  the  following  claims  of  merit  for 
this  instrument,  which  also  combines  an  indirect  ophthalmo- 
scopic adjustment. 

"This  instrument  makes  use  of  the  direct  method  of  retinos- 
copy,  the  most  valuable  of  methods  for  testing  the  refraction  of 
the  eye,  because  (i)  it  is  an  objective  test  and  requires  no 
catechism  of  the  patient,  and    (2)   because  of  its  wonderful 


VARIOUS    INSTRUMENTS    USED    IN    SKIAMETRY  ID5 

exactness.  But  the  instrument  offers  special  advantages  to  the 
retinoscopist  above  those  possibly  obtainable  by  the  hand  method. 
These  are  chiefly  as  follows : 

"ist.  The  instrument  introduces  no  new  principle,  but 
simplifies  the  general  method  of  skiascopy  as  practiced  in  the 
dark  room  with  a  plane  mirror.  The  same  rules  that  govern 
in  the  hand  method  govern  also  in  the  use  of  the  instrument, 
and  those  who  are  experienced  in  the  test  have  nothing  to 
unlearn. 

"2d.  The  instrument  may  be  operated  in  a  Hght,  airy 
room  or  the  regular  office  for  refraction  work.  This  enables 
the  operator  to  combine  Avith  it  the  fogging  method  for  re- 
ducing ciliary  spasm.  This  combination  is  impossible  in  dark 
room  skiascopy,  for  darkening  the  room  to  brighten  the  reflex 
obscures  the  distant  object  by  which  the  accommodation  is 
properly  fogged. 

"3d.  The  mirror  is  so  fixed  that  it  may  be  tilted  true  to 
any  given  meridian  and  so  arranged  that  it  may  be  rotated  to 
any  meridian  and  remain  stationary  in  that  meridian  as  long  as 
desired.  This  gives  a  far  greater  degree  of  accuracy  in  locat- 
ing the  two  principal  meridians  in  an  astigmatic  eye  than  is 
possible  with  an  ordinary  hand  retinoscope,  as  used  in  the 
method  hitherto  practiced. 

"4th.  The  light,  mirror,  patient's  eye  and  observer's  eye 
are  always  in  their  exact  relative  positions,  and  there  is  no  time 
wasted,  therefore,  in  finding  the  patient's  eye  or  keeping  it  in 
view  when  found.  Moreover,  having  the  distances  all  fixed 
once  and  for  all,  the  operator  does  not  need  to  keep  them 
perpetually  in  mind  or  think  of  them  at  all.  He  can  devote 
his  whole  attention  to  watching  the  movements  of  the  reflex 
and  shadow  and  operating  the  lens  discs  to  get  the  result  he 
requires. 


l66  VARIOUS    INSTRUMENTS    USED    IX    SKIAMETRV 

"5th.  There  are  no  deductions  or  additions  to  be  made 
when  the  right  lens  is  found,  for  the  distances  are  all  neu- 
tralized to  infinity  with  plus  lenses  fixed  in  the  instrument. 
The  point  of  reversal  of  an  emmetropic  observed  eye  is  always 
about  one  inch  back  of  the  mirror,  or  where  the  cornea  of  the 
observer's  eye  will  be  when  the  best  view  of  the  pupil  is 
obtained. 

"6th.  There  are  arranged  in  the  instrument  two  large  ro- 
tating discs  in  which  are  fixed  batteries  of  plus  and  minus 
lenses.  These  discs  may  be  so  rotated  as  to  bring  any  desired 
plus  or  minus  lens  before  the  patient's  eye.  This  obviates  the 
necessity  of  reaching  forward  to  change  the  lenses  from  the 
trial  case  during  the  examination — one  of  the  most  inconvenient 
features  of  open  retinoscopy,  as  generally  practiced. 

"7th.  The  lights  used  may  be  changed  in  one  minute  from 
oil  to  gas  or  electric,  as  they  are  interchangeable." 

The  De  Zeng  Combined  Optometer,  Phorometer  and  Ski- 
ameter, manufactured  by  the  De  Zeng-Standard  Co.,  Camden, 
N.  J.,  is  another  late  invention  designed  for  use  in  both  objec- 
tive and  subjective  optometry,  also  for  muscle  measuring  and 
exercising  as  well. 

Fig.  69  shows  the  general  appearance  of  the  head  of  this 
instrument,  which  can  be  mounted  either  on  a  bracket  or  on  a 
stand. 

The  manufacturers  set  forth  the  merits  of  this  compre- 
hensive device  in  the  following  claims : 

"This  new  instrument  is  a  perfect  combination  of  our  well 
known  Phoro-Optometer  and  a  binocular  quadruple  series  of 
plus  and  minus  spherical  lenses  mounted  in  light  disk  form. 
It  is  exceedingly  compact  and  complete,  is  unusually  light,  well 
finished  and  is  the  best  all  around  instrument  ever  offered  for 
Objective  and  Subjective  Refraction  and  Muscle  Work. 

"The  lenses   are   all   one   inch  in  diameter,   are   accurately 


VARIOUS    INSTRUMENTS    USED    IN    SKIAMETRY 


167 


ground  and  centered,  and  may  be  brought  into  operative  posi- 
tion separately  or  in  combination  as  desired.  The  first  disk 
facing  the  operator  contains  o,  .25,  .50.  .75,  i.oo,  1.25,  1.50 
and  1.75  in  plus  spheres;  the  second  disk  carries  the  same 
numbers  in  minus  spheres,  the  third  disk  holds  the  first  series 
of  auxiliary  numbers,  and  by  a  partial  rotation  outward  from 
zero,  2.00,  4.00  and  6.00  in  plus  are  obtained,  while  an  inward 
movement   from   zero  gives   2.00,  4.00,  6.00  and   8.00  in   the 

Fig.  69. 


DE   ZENG  S    OPTOMETER,    PHOROMETER  AND    SKIAMETER. 


minus.  The  fourth  disk  contains  the  second  series  of  auxiliary 
numbers,  and  by  a  partial  rotation  of  the  disk  downward  from 
the  horizontal  position  of  the  Controlling  Arm,  which  is  lo- 
cated at  zero,  plus  .12,  8.00  and  1.50  are  obtained,  while  an 
upward  movement  from  zero  gives  minus  .12,  10.00  and  blank. 
The  plus  1.50  lens  is  for  use  in  Retinoscopy  at  a  26-inch  work- 
ing distance,  which  is  within  arm's  reach  of  the  Instrument. 
By  combining  the  contents  of  the  first  disk  with  the  positive 
auxiliary   numbers   in   the   third   and   fourth  disks,   all  of  the 


l68  VARIOUS    INSTRUMENTS   USED   IN    SKIAMETRY 

positive  equivalents  from  .12  to  7.87  inclusive  are  obtainable  in 
eighths,  and  from  .25  to  15.75  inclusive  in  quarters.  The 
negative  equivalents  are  likewise  obtained  by  employing  the 
second  disk  in  conjunction  with  the  minus  auxiliaries  carried 
by  the  third  and  fourth  disks,  but  in  the  minus  numbers  the 
range  is  extended  to  9.87  in  eighths  and  to  19.75  '^^  quarters." 

With  the  exception  of  the  author's  instrument  which,  as 
will  presently  be  seen,  is  a  radical  departure  in  almost  every 
way  from  those  just  referred  to,  this  completes  the  list,  although 
there  are  still  quite  a  number  of  other  instruments  which 
embrace  the  principles  here  shown, 

Jackson  in  his  valuable  book  on  Skiascopy,  in  speaking 
of  the  use  of  disc  lenses  (page  109)  says:  *'But  even  in  this 
case,  the  fact  that  there  is  a  complete  break  between  the 
appearances  represented  by  one  lens,  and  the  appearances 
present  by  the  use  of  the  lens  next  stronger  or  zveaker,  makes 
the  information  obtained  less  valuable  and  satisfactory  than 
that  derived  from  the  movement  of  the  surgeon's  eye  from 
one  position  to  another,  which  allows  him  to  zvatch  the  dif- 
ferent appearances  of  light  and  shade  as  they  pass  gradually 
into  each  other."  This  "movement  of  the  surgeon's  eye"  to 
which  he  refers  has  since  been  practically  duplicated  by  mak- 
ing the  lens  action  mobile  instead  of  fixed,  thus  securing 
superior  results  with  less  effort. 

From  the  instrument  of  Grain  to  that  of  the  Geneva  it 
may  be  observed  that  the  proper  adjustment  of  the  patient's 
head  by  means  of  chin  rests,  etc.,  is  an  important  item,  and, 
with  the  exception  of  the  oculometroscope  type  of  instrument 
they  all  require  separate  adjustment  for  each  eye.  Besides, 
not  one  of  them  is  arranged  for  magnifying  the  patient's  pupil, 
no  matter  how  small  it  may  be  nor  how  great  the  difficulty  of 
accurately  noting  the  action  of  its  shadow. 

All  of  the  disc  type  of  instruments  are  designed  to  work 
at  one  fixed  distance,  no  latitude  being  allowed  unless  they 


author's  skiameter  169 

are  operated  in  an  awkward  manner,  and  this  of  course  limits 
their  use  to  the  static  method  only,  barring  out  the  dynamic, 
which  of  the  two  is  really  the  more  valuable.  Therefore,  all 
monocular  testing  instruments  are  of  little  service  in  thorough 
skiametric  work. 

Wiirdemann's  device  is,  like  the  use  of  trial  lenses,  most 
excellent  in  theory,  but  in  practice  its  shortcomings  seem  to 
be  many.  In  the  practical  workings  of  all  disc  devices  their 
use  usually  proves  of  considerable  assistance  to  an  examiner, 
especially  when  the  disc  can  be  controlled  by  rods,  but  all  disc 
instruments,  it  is  feared,  will  eventually  be  relegated  to  the 
company  of  the  many  other  optometric  devices  which  have  been 
weighed  in  the  balance  and  found  wanting.  However,  it  is 
for  others  to  judge  of  this  after  they  have  informed  themselves 
regarding  the  advantages  gained  by  the  use  of  the  next  instru- 
ment to  which  attention  is  here  called. 

THE  AUTHOR'S  SKIAMETER.  This  little  device, 
among  its  other  features,  was  designed  to  accomplish  a  pur- 
pose similar  to  that  of  the  various  disc  contrivances  in  over- 
coming the  necessity  for  having  examiners  change  position 
every  time  a  lens  needed  changing.  Like  Wiirdemann's  device, 
too,  it  was  designed  as  a  hand  instrument,  so  as  to  make  the 
adjustments  rapid  and  easy,  but  unlike  Wurdemann's  rack,  it 
was  arranged  to  be  so  placed  that  its  position  should  be  as 
secure  as  that  of  a  trial  frame. 

Enlargement  of  ocular  pupils  was  sought  for  and  achieved, 
together  with  mobile  lens  action.  Variety  in  methods  of  oper- 
ating was  not  so  much  a  first  consideration  as  it  was  an  after- 
thought. The  construction  of  the  instrument,  however,  needed 
very  little  alteration  after  dynamic  skiametry  was  developed, 
although  the  addition  of  this  method  to  the  value  of  the  instru- 
ment has  been  found  too  great  to  be  estimated  by  figures. 

Binocular  action  was  also  an  original  feature;  then  sim- 


170  AUTHOR  S    SKIAMETER 

plicity;  not  only  simplicity  of  construction  and  action,  but 
simplicity  of  operation.  Fig.  70  shows  the  mechanical  arrange- 
ment of  the  instrument  and  the  manner  of  the  adjustment  of 
its  lens  system. 

Two  convex  and  two  concave  cylindric  lenses  of  seven 
diopters  each  are  mounted  in  cells  A  and  B,  and  A  and  B 
prime,  with  their  axes  at  right  angles  to  each  other,  each  lens 
being  slightly  inclined  from  the  perpendicular  on  its  meridional 


Fig.  70. 


H. 


RGnUZE: 


0. 

CONSTRUCTIVE  PRINCIPLE  OF  AUTHOR's  SKIAMETER. 

axis.  The  two  concave  lenses  are  stationary  while  the  two 
convex  ones  are  made  movable.  The  cells  of  the  latter  slide 
on  rod  H,  being  controlled  by  a  doubled  cord  C,  D,  thirty-six 
inches  in  length,  this  cord  passing  over  pulley  F.  The  cord's 
length  being  always  the  same,  an  operator  has  merely  to  turn 
his  hand  at  the  wrist  in  order  to  obtain  full  control  of  the 
refractive  changes  of  the  instrument. 

In  the  use  of  convex  cylindric  lenses  it  was  found  that 
by  placing  each  cell  on  a  sliding  block,  such  as  shown  by  K 
and  E,  and  by  then  using  a  hook  the  operator  could  unfasten 


AUTHOR  S    SKIAMETER  I7I 

them  while  working  at  a  distance  by  merely  moving  his  hand 
a  few  inches  to  one  side.  The  cylindric  lenses  used  in  this 
way  could  also  be  made  to  serve  a  double  purpose ;  for  when 
used  together  they  acted  as  a  single  spheric  lens  does,  but  when 
used  singly,  or  unlocked,  they  acted  as  simple  cylinders. 

Another  valuable  principle  was  also  discovered  and  made 
use  of.  It  was  found  that  as  the  plus  cylinders,  A  and  B 
prime,  were  moved  away  from  the  minus  cylinders,  A  and  B, 

Fig.  71. 


AUTHOR  S    SKIAMETER,    WITHOUT    BASE. 

any  object,  such  as  a  patient's  eye,  when  placed  close  up  to 
the  concave  lenses,  would  be  magnified  by  the  convex  ones,  just 
as  though  a  plain  seven-diopter  convex  spheric  lens  had  been 
used,  this  magnification  taking  place  without  causing  the  least 
interference  in  the  refraction  of  the  four  lenses  while  they  were 
being  used  as  a  lens  series  to  produce  mobility  of  action. 

Other  attachments  comprise  a  self-adjusting  brow  rest  to 
give  the  instrument  stability,  a  handle,  a  base  and  a  means  for 
separating  the  two  tubes.     The  large  holes  now  in  the  top  of 


172  AUTHOR  S   SKIAMETER 

the  tubes  of  the  latest  model  instrument  facilitate  the  cleaning 
of  the  lenses,  whose  cells  are  all  attached  to  blocks  on  the  slide 
rods.  The  minus  cylindric  lenses  are  secured  in  position  by 
a  set  screw  in  the  block  holding  cell  B. 

Fig.  71  shows  the  instrument  complete,  with  its  auxiliary 
lens  disc  containing  three  sphericals,  i.  e.,  —  i.  —  3.  and  — 
6.  D.,  to  be  used  in  converting  the  instrument  from  the  static 
to  the  dynamic  method,  also  for  changing  the  total  refraction 
from  plus  to  minus,  as  occasion  demands. 


CHAPTER  XL 

Questions  and  Answers  Pertaining  to  Static  and  Dy- 
namic Skiametry  and  Correlated  Subjects,  With 
Pertinent  Remarks  Emphasizing  the  Salient  Points 
Involved. 

There  is  perhaps  no  better  way  in  which  to  fixedly  impress 
upon  the  mind  of  the  student  the  underlying  principles  gov- 
erning ocular  skiametry  than  to  require  him  to  answer  a  series 
of  questions  embracing  the  salient  points  involved  in  the  sub- 
ject. The  remarks  following  each  answer  given  in  this  chapter, 
though  sometimes  a  repetition  of  matter  contained  in  previous 
chapters,  will  also  serve  to  emphasize  the  principal  points 
involved.  But  to  avoid  creating  any  wrong  impressions  it  may 
be  well  to  preface  these  questions  and  answers  by  calling  atten- 
tion once  more  to  the  fact  that  the  subjects  are  here  treated 
in  a  purely  theoretic  manner.  For  instance :  If  by  dynamic  ski- 
ametry the  intrinsic  and  extrinsic  muscles  are  not  in  a  "i  to  3" 
relationship  then  the  refractive  findings  will  not  be  the  same  as 
though  these  muscles  maintained  this  so-called  "standard" 
harmony. 

One  of  the  greatest  points  of  merit  of  skiametry  is  that  it 
always  tells  the  exact  truth,  even  though  examiners  cannot 
invariably  interpret  this  aright,  but  when  a  shadow  moves 
either  with  or  against  a  mirror's  movement  it  indicates  that  the 
conjugate  focus  of  the  emerging  ray  is  either  posterior  or 
anterior  to  the  examiner's  position  of  observation. 

The  cause  influencing  focal  length  of  the  emerging  rays  is 
quite  a  diflferent  question  from  that  of  reading  the  action  of 
the  shadow,  for  what  is  known  by  the  names,  latent  hyperopia 


174  QUESTIONS,    ANSWERS    AND    REMARKS 

and  sub-normal  presbyopia,  may  be  merely  a  changed  relation- 
ship between  accommodation  and  convergence  that  is  peculiar 
to  the  case  under  examination. 

Skiametry  merely  determines  the  state  of  the  refraction  at 
any  given  point,  the  same  as  phorometry  can  be  made  to  show 
the  co-ordination  of  the  two  eyes  for  any  point  of  convergence. 
With  skiametry,  however,  the  examiner  is  largely  independent 
of  the  patient's  reliability,  whereas,  with  phorometry  it  depends 
entirely  upon  a  patient's  replies  to  set  questions  which  thus 
form  a  very  uncertain  quantity. 

In  the  questions  following  No.  24  it  will  be  noted  that 
•fixation  is  never  placed  nearer  the  patient  than  that  of  observa- 
tion. Theoretically  it  ought  not  to  make  any  difference  what 
relationship  these  two  factors  bear  to  one  another,  but  in  prac- 
tical application  it  will  be  found  that  attempted  fixation  for  a 
point  inside  of  the  patient's  pimctum  proximiim  will  be  pro- 
ductive of  very  uncertain  results  until  the  correction  nears  the 
point  where  fixation  and  observation  become  equal. 

Where  fixation  is  beyond  the  point  of  observation  then  more 
reliable  findings  are  obtained,  but  for  extreme  accuracy  of 
measurement  it  is  necessary  that  fixation  and  observation  should 
be  the  same,  lenses  being  used  for  altering  the  focal  length  of 
the  emergent  rays  while  the  examiner  remains  in  a  fixed  po- 
sition. 

Familiarity  with  both  ray-value  and  lens-value  methods 
enable  an  examiner  to  cover  a  much  wider  range  of  measure- 
ments, also  to  work  with  greater  speed  and  to  secure  data  that 
materially  aids  in  the  correct  formation  of  that  judgment  which 
predetermines  success. 

Question  No.  i.  Reduce  and  transpose  the  following 
formula : 

—  0.50  D.  S.  C  +  I-  E).  C.  axis  15  C  +  0.25  D.  S. 
C  —  0.75  D.  C.  axis  105. 


QUESTIONS,    ANSWERS    AND    REMARKS  I75 

Write  the  answer  three  ways. 

Answer  No.  i. 

+  0.75  D.  C.  C  —  I.  D-  C.  axis  105. 
+  0.75  D.  S.  C  —  1-75  D-  C.  axis  105. 
—  I.  D.  S.  C  +  1-75  D.  C.  axis  15. 

Remarks,  No.  i.  The  reduction  and  transposition  of  lenses 
belongs  properly  under  theoretic  optics,  but  its  relation  to  ^^i- 
ametry  is  so  pronounced  that  unless  a  student  makes  himself 
master  of  at  least  one  reliable  system  his  progress  in  shadow- 
testing  will,  indeed,  be  difficult. 

The  author's  system  of  converting  all  lens  values  into 
cylindric  equivalents  and  then  reconstructing  these  into  desired 
combinations  will  give  the  best  forms  for  the  purposes  needed 
and  will  be  found  one  of  the  simplest  ways  of  dealing  with  this 
complex  problem. 

By  "best  forms,"  it  may  be  added,  that  in  this  age  of  atten- 
tion to  details,  it  frequently  happens  that  an  examiner  desires 
to  write  his  formula  so  as  to  obtain  a  meniscus  effect  in  the 
completed  lens,  or  else  he  may  prefer  to  so  combine  his  hi-focals 
that  the  segment  will  always  be  on  the  inside  of  the  lens.  The 
form  of  reduction  and  transposition  described  herein  makes 
this  possible,  hence  its  importance  to  the  student. 


Question  No.  2.  With  a  schematic  eye  set  at  cmmetropia 
and  having  a  -|-  0.75  D.  S.  lens  before  it,  how  many  inches 
away  will  the  skiametric  reversal  point  be  ? 

Answer  No.  2.    Fifty-three  inches. 

Remarks,  No.  2.  This  is  a  case  of  simple  artificial  myopia. 
In  the  living  eye,  however,  if  the  patient  had  unconsciously 
looked  at  any  object  within  infinity,  say  at  fifteen  feet  away, 
then  accommodative  myopia  would  be  a  factor,  and  the  total 
myopia  present  would  be  i.  D.,  making  the  point  of  reversal 
at  forty  inches  instead  of  at  fifty-three. 


176  QUESTIONS,    ANSWERS    AND   REMARKS 

Twenty  feet  is  usually  considered  as  infinity  in  practical 
optometry,  but  for  real  accurate  measurements  this  classification 
will  be  found  untrustworthy,  as  a  lens  of  0.12  D.  has  a  focal 
length  of  over  twenty-six  feet,  and  in  these  days  formulas 
calling  for  0.12  D.  lens-power  are  not  uncommon. 


Question  No.  3.  With  a  schematic  eye  set  for  i.  D.  of 
myopia,  and  having  a  lens  —  i,  D.  C.  axis  90  before  it,  how 
far  away  will  the  skiametric  point  of  reversal  be  in  the  vertical 
meridian  ? 

Answer  No.  3.    Forty  inches. 

Remarks,  No.  3.  It  is  well  known  that  in  an  emmetropic 
eye  a  plus  lens  held  before  it  creates  myopia.  If  the  lens  is 
minus,  however,  then  the  artificial  error  is  hyperopia.  And  if 
the  lenses  used  are  spherics  then  the  error  is  in  all  meridians, 
but  if  cylindrics  are  used  then  the  error  is  only  in  the  meridian 
at  right  angles  to  the  axis  of  the  lens  employed. 

In  question  No.  3  the  required  myopia  for  forty  inches 
working  distance  is  obtained  by  slightly  lengthening  the  sche- 
matic eye,  and  thus  what  might  be  considered  as  true  myopia 
is  a  factor. 

The  use  of  a  —  i.  D.  C.  lens,  axis  vertical,  would  serve  to 
neutralize  this  true  myopia  in  the  horizontal  meridian,  thereby 
causing  the  rays  to  emerge  parallel,  but  the  rays  in  the  vertical, 
not  having  been  interfered  with,  continue  to  converge  to  a  point 
I.  D.,  or  forty  inches  away. 


Question  No.  4.  With  a  schematic  eye  set  for  i.  D.  of 
myopia,  what  lenses  should  be  added  to  artificially  produce  a 
mixed  astigmatic  error  equal  to  —  1.25  D.  S.  C  +  2.  D.  C. 
axis  45  ? 


questions,  answers  and  remarks  i77 

Answer  No.  4. 

+  1.25  D.  S.  C  —  2.  D.  C.  axis  45  or  —  0.75  D.  S. 
C  +  2.  D.  C.  axis  135. 

Remarks,  No.  4.  As  myopia  is  produced  with  a  plus  lens 
and  hyperopia  with  a  minus  one  then  all  that  is  required  in  the 
above  case  is  to  use  lenses  of  the  same  strength  but  opposite 
kind,  and  if  for  any  reason  these  lenses  are  not  available  then 
the  second  formula,  given  in  the  answer,  can  be  made  use  of, 
this  being  obtained  by  transposition. 

In  a  living  eye  the  artificial,  or  "working,"  myopia  would 
have  to  be  produced  by  a  4-  i-  D-  S.  lens,  and  then  this  quan- 
tity would  have  to  be  taken  into  consideration  in  the  final 
analysis.  But  with  schematic  eyes  the  artificial  myopia  can  be 
made  into  true  myopia  by  simple  adjustment  in  length,  so  for 
purpose  of  practice  work  the  question  of  "working  quantity" 
can  be  temporarily  eliminated. 


Question  No.  5.  What  is  the  difiference  between  tonic  and 
clonic  spasm? 

Answer  No.  5.  Tonic  spasm  is  a  persistent,  involuntary 
contraction  of  a  muscle,  whereas  clonic  spasm  is  an  intermittent 
contraction. 

Remarks,  No.  5.  It  would  seem  to  matter  very  Httle  to  an 
examiner  what  the  character  of  the  spasm  was  that  confronted 
him  if  it  was  not  for  the  theoretic  side  of  his  work.  Tonic 
spasms  are  met  most  frequently  in  hyperopic  cases,  and  clonic 
in  myopic  ones,  habit  forming  a  marked  factor.  These  two 
kinds  of  spasms,  then,  are  probably  responsible  for  the  frequent 
overcorrections  found  in  myopia  and  for  the  undercorrections 
found  in  hyperopia,  therefore  all  examiners  should  adopt  such 
methods  as  will  eliminate  the  influence  of  these  uncertain 
factors. 


178  QUESTIONS,    ANSWERS    AND   REMARKS 

Question  No.  6.  How  many  degrees  of  convergence  does 
a  hypermetrope  of  2.  D.  suppress  when  his  accommodation  is 
adjusted  for  infinity? 

Answer  No,  6.    About  six  degrees. 

Remarks,  No.  6.  For  ease  of  comprehension  the  "i  to  3" 
relationship  between  accommodation  and  convergence  will  per- 
haps be  found  better  than  where  meter  angles  are  used.  Thus, 
in  question  No.  6,  it  is  easy  to  understand  that  if  2.  D.  of 
accommodation  is  used  to  overcome  the  hypermetropia,  then 
2  times  3  degrees  equals  6,  and  if  binocular  parallelism  is  neces- 
sary of  the  correct  registration  of  rays  of  light  from  infinity, 
then  suppression  of  convergence  must  be  made.  The  intrinsic 
muscles  in  this  case  dictating  to  the  extrinsic  ones. 


Question  No.  7.  How  many  diopters  of  accommodation 
does  a  myope  of  2.  D.  exert  when  he  converges  to  a  point  call- 
ing for  9  degrees? 

Answer  No.  7.    One  diopter. 

Remarks,  No.  7.  The  reasoning  is  simple ;  if  9  degrees  of 
convergence  call  for  3.  D.  of  accommodation  and  2.  D.  of 
myopia  neutralizes  2.  D.  of  accommodation,  then  the  difference 
between  the  accommodation  that  ought  to  be  used  and  the 
accommodation  that  is  not  used  gives  the  amount  of  accommo- 
dation that  is  used. 

If  A  owes  B  $3,  and  B  owes  C  $2,  then  if  C  owes  A  $2, 
there  is  a  chance  to  settle  these  differences  by  the  payment  of 
only  $1,  all  of  which  can  be  worked  out  by  a  little  figuring. 


Question  No.  8.  What  is  the  difference  between  static 
and  dynamic  skiametry? 

Answer  No.  8.  "Static"  skiametry  is  where  fixation  is  at 
infinity,  while  "dynamic"  skiametry  is  where  fixation  is  within 
infinity. 


QUESTIONS,    ANSWERS    AND   REMARKS  179 

Remarks,  No.  8.  The  above  definition  is  probably  as  short 
as  a  technical  one  can  be  given.  This  question  is  asked  so 
often,  however,  that  perhaps  it  ought  to  be  answered  in  a  num- 
ber of  ways. 

Static  skiametry  is  where  accommodation  is  supposed  to  be 
relaxed.  Dynamic  skiametry  is  where  it  is  supposed  to  be 
exerted. 

The  word  "supposed"  is  used  because  in  static  skiametry 
accommodation  is  rarely  ever  fully  relaxed,  and  in  dynamic 
skiametry  accommodation  is  rarely  ever  fully  exerted,  spasm 
in  relaxation  and  lag  in  exertion,  are  both  to  be  reckoned  with. 

Static  skiametry  can  be  used  for  determining  the  patient's 
easy  adjustment  of  his  ocular  muscles  for  distance,  while 
dynamic  skiametry  can  be  used  for  determining  the  easy  ad- 
justment of  the  ocular  muscles  for  reading  or  near  work. 


Question  No.  9.  By  static  skiametry  with  fixation  at 
infinity  and  observation  at  26  inches,  what  should  be  the 
strength  of  the  lens  used  to  create  the  working,  or  artificial, 
myopia  ? 

Answer  No.  9.    -\-  1.50  D.  S. 

Remarks,  No.  9.  At  whatever  distance  an  examiner  op- 
erates in  the  static  method  he  must  be  careful  to  know  its  exact 
dioptric  value.  Thus,  if  his  observation  is  made  at  10  inches 
he  must  have  an  artificial  myopia  of  4.  D.  If  at  20  inches 
then  2.  D.,  and  so  on. 

If,  however,  he  uses  a  2.  D.  working  quantity  and  care- 
lessly makes  his  observation  from  a  point  18  inches  from  his 
patient,  then  his  findings  will  show  an  overcorrection  of  0.25  D., 
for  18  inches  calls  for  a  lens  quantity  of  -}-  2.25  D. 


Question  No.  10.    By  static  skiametry  if  a  -|-  2.25  D.  S. 


l8o  QUESTIONS,    ANSWERS    AND    REMARKS 

lens  in  front  of  an  eye  causes  reversal  in  all  meridians  at  40 
inches  observation,  what  is  the  apparent  error? 

Answer  Xo.  10.     1.25  D.  of  hyperopia. 

Remarks,  Xo.  10.  The  word  "apparent"  is  used  here  ad- 
visedly. A  static  examination  made  at  40  inches,  or  any  other 
distance,  gives  the  exact  refraction  under  the  existing  condi- 
tions, but  often  these  "conditions"  are  based  on  an  adjustment 
between  accommodation  and  convergence  which  gives  a  re- 
fractive finding  that  is  not  in  harmony  with  the  one  found 
for  reading  distance,  therefore  it  will  be  seen  that  accuracv 
in  judgment  calls  for  measurements  made  at  various  distances. 


Question  X'o.  ii.  By  static  skiametry,  if  a  patient  has  i.  D. 
of  hyperopia,  where  will  the  point  of  reversal  be  in  all  meridians 
when  a  +  2.75  D.  S.  lens  is  used? 

Answer  No.  ii.    At  twenty-two  inches. 

Remarks,  Xo.  ii.  In  this  case  the  patient's  error  neu- 
tralizes, or  absorbs,  i.  D.  S.  of  the  artificial  myopia,  leaving  only 
1.75  D.  remaining. 

If  the  patient's  error  had  been  myopic,  instead  of  hyperopic, 
then  the  total  would  have  been  an  increase  instead  of  a 
decrease. 

Careful  attention  must  always  be  given  to  the  kind  of 
myopia  present,  whether  it  is  true  or  artificial,  and  then  to  keep 
in  mind  that  hyperopia  neutralizes  myopia,  and  that  myopia 
does  the  same  for  hyperopia. 


Question  X'o.  12.  By  static  skiametry  without  any  lenses 
on,  if  reversal  is  found  in  all  meridians  at  13  inches  from  pa- 
tient's eyes,  what  is  the  error? 

Answer  X'o.  12.    3.  D.  of  myopia. 


QUESTIONS,    ANSWERS    AND   REMARKS  l8l 

Remarks,  No.  12.  It  will  be  seen  from  the  above  that  one 
of  the  easiest  ways  to  estimate  myopia  is  by  a  tape  measure  in 
place  of  lenses.  In  hyperopia,  however,  the  use  of  lenses  is 
imperative,  for  it  will  be  borne  in  mind  that  myopia  of  some 
kind,  true,  artificial  or  accommodative,  must  be  present  in  order 
to  make  use  of  the  principles  of  shadow-testing. 


Question  No.  13.  By  static  skiametry  if  a  patient  has 
I.  D.  of  myopic  astigmia  in  the  vertical  meridian,  how  many 
inches  away  will  the  point  of  reversal  be  in  the  horizontal 
meridian  when  he  uses  a  -|-  i,  D.  S.  lens? 

Answer  No.  13.    Forty  inches. 

Remarks,  No.  13.  If  the  student  will  keep  in  mind  that  all 
eyes  must  be  measured  in  two  meridians,  that  of  greatest  and 
least  refraction,  the  above  will  resolve  itself  into  a  simple  case 
of  reduction.  The  two  chief  axes  are  90  and  180,  and  the 
-|-  I.  D.  S.  lens  creates  artificial  myopia  of  i.  D.  The  reduc- 
tion then  is  as  follows : 

Axis  po 

+  I. 


Axis 

180 

+ 

I. 

+ 

I. 

+    1.  +2. 

The  refraction  in  the  vertical  meridian  shows  a  reversal 
point  at  20  inches. 

The  student  must  not  forget  that  minus  neutralizes  plus, 
and  that  myopia  therefore  indicates  a  plus  condition,  because 
it  takes  minus  lenses  to  counteract  it. 


Question  No.  14.    By  static  skiametry  at  40  inches  obser- 
vation, il  a  -j-  I-  D.  lens  causes  reversal  in  the  vertical  meridian 


l82  QUESTIONS,    ANSWERS    AND    REMARKS 

and  it  takes  a  -|-  2.  D.  to  cause  reversal  in  the  horizontal,  what 
is  the  error? 

Answer  No.  14.    -{-  1.  D.  C.  axis  90. 

Remarks,  No.  14.    This  is  a  case  for  transposition. 
Axis  go  Axis  180 

+  2.  +1. 

and  this  equals  -\-  i.  D.  S.  3  +  i.  D.  C.  axis  90.  Adding 
—  I.  D.  S.  for  the  neutralization  of  the  artificial  myopia,  the 
error  then  becomes  -(-  i,  D.  of  hyperopia  astigmia  in  the  hori- 
zontal meridian,  with  the  axis  in  the  vertical. 

Students  must  be  careful  not  to  get  axis  and  error  confused, 
for  an  eye  that  measures  52.  D.  in  the  vertical  meridian  and 
51.  D.  in  the  horizontal  could  be  made  52.  D.  in  all  meridians 
by  the  use  of  a  cylindric  lens  of  -|-  i.  D.  axis  vertical. 


Question  No.  15.  By  static  skiametry,  if  a  patient  has 
compound  hyperopia  astigmia  that  can  be  neutralized  with  a 
lens  of  +  I.  D.  S.  3  +  i.  D.  C.  axis  90,  where  will  the  points 
of  reversal  be  in  the  horizontal  and  vertical  meridians  when  he 
uses  a  -{-  3.  D.  S.  lens? 

Answer  No.  15.  Forty  inches  in  the  horizontal  and  twenty 
inches  in  the  vertical. 

Remarks,  No.  15.  This  is  another  case  of  reduction.  The 
student  remembering  that  if  myopia  is  a  plus  condition  then 
hyperopia  must  be  a  minus  one,  and  on  this  basis  the  reduction 
would  be  expressed  as  follows : 

Axis  po  Axis  180 

—  I.  —  I. 

—  I. 

+  3-  -+    3- 

+  I.D.  +2.D. 


QUESTIONS,    ANSWERS    AND   REMARKS  183 

Calling  the  error  plus  and  considering  the  3.  D.  lens  as 
artificial  myopia  the  reduction  could  be  figured  another  way  and 
obtain  the  same  results : 

Axis  go  Axis  180 

+  1.  +1. 
+  I. 

—  3-  —  3. 


—  i.D.  —  2.D. 

for  if  it  takes  a  —  i.  D.  C.  axis  90  to  correct  the  error  in  the 
horizontal  meridian  then  the  convergence  is  for  40  inches, 
similar  reasoning  applying  to  the  vertical  where  the  focus  is  20 
inches. 


Question  No.  16.  By  static  skiamctry  with  a  +  i.  D.  S. 
lens  before  the  patient's  eye,  if  reversal  occurs  in  the  vertical 
meridian  at  22  inches,  and  in  the  horizontal  at  32  inches,  what 
is  the  error? 

Answer  No.  16.    —  0.25  D.  S.  C  —  0-5o  D.  C.  axis  180. 

Remarks,  No.  16.  An  analysis  of  this  case  shows  artificial 
myopia  to  equal  i.  D.  If  reversal  occurs  in  the  vertical  merid- 
ian at  22  inches  then  the  refraction  must  be  1.75  D.  of  total 
myopia.  Deducting  i.  D.  of  artificial  myopia  leaves  a  true 
myopia  of  0.75  D.  in  this  meridian. 

In  the  horizontal  meridian  if  reversal  occurs  at  32  inches 
the  total  refraction  for  this  meridian  is  1.25  D.  Deducting 
the  artificial  as  before  leaves  a  true  myopia  of  0.25  D.  C.  90, 
and  by  transposition  the  error  is  found  to  be  neutralized  by 
—  0.25  D.  S.  C  —  0.50  D.  C.  180. 


Question  No.  17,     If  52.  D,  S.  represents  the  total  re- 
fraction of  a  standard  eye,  where  will  the  points  of  reversal  be 


184  QUESTIONS^    ANSWERS    AND   REMARKS 

by  static  skiametry  in  an  eye  whose  measurement  in  the  hori- 
zontal meridian  is  51.  D.  and  53.  D.  in  the  vertical,  a  +  2.  D.  S. 
lens  being  used? 

Answer  No.  17.  Horisontal  at  40  inches,  vertical  at  13 
inches. 

Remarks,  No.  17.  Of  course  it  is  known  that  there  is  no 
such  thing  as  a  standard  eye,  any  more  than  there  is  a  standard 
ear  or  a  standard  tooth,  etc.,  but  for  the  purpose  of  trying  to 
think  in  refractive  parlance  52.  D.  has  been  suggested  as  repre- 
senting the  average  emmetropic  eye.  This  being  the  case,  a 
meridian  that  shows  only  51,  D.  is  deficient  i.  D.  and  is  called 
hyperopic.  The  meridian  showing  53.  D.  is  over  the  required 
refraction  and  is  therefore  plus  i.  D.  or  "myopic."  Taking 
these  into  consideration  the  problem  is  expressed  thus : 

Axis  po  Axis  180 

-  I.  +1. 

+  2.  +2. 


+  I.  +3. 


Question  No.  18.  In  a  patient  having  3.  D.  amplitude  of 
accommodation,  how  close  to  the  eye  (in  inches)  can  a  measure- 
ment be  reliably  made  by  dynamic  skiametry? 

Answer  No.  18.    Not  nearer  than  13  inches. 

Remarks,  No.  18.  Bonders  is  authority  for  the  statement 
that  the  near  point  of  distinct  vision  in  a  child  10  years  of  age 
is  two  and  three-quarter  inches  from  the  eyes.  This  distance 
reduced  to  diopters  gives  what  is  called  amplitude  of  accommo- 
dation equal  to  14.  D.  This  amplitude  diminishes  as  age  ad- 
vances, until  at  about  47  years  of  age  the  amplitude  is  only 
3.  D.,  hence  it  is  wise  for  an  examiner  to  keep  these  facts  well 
in  mind  when  using  dynamic  skiametry,  then  the  error  will  not 


QUESTIONS,    ANSWERS    AND   REMARKS  185 

become  confused   with  presbyopia  when  the  "p  p"  has  been 
reduced  to  13  inches. 


Question  No.  19.  In  a  patient  ten  years  of  age  showing 
convergent  strabismus,  how  close  to  the  eye  should  dynamic 
measurements  be  made? 

Answer  No.  19.  Ten  inches  is  generally  near  enough, 
because  it  is  inside  of  the  usual  reading  point  of  the  patient. 

Remarks,  No  19.  When  strabismus  is  present,  however,  it 
indicates  a  marked  disturbance  between  accommodation  and 
convergence,  and  the  examiner  has  every  reason  to  suspect  a 
pronounced  error  of  refraction  which,  by  the  way,  is  not 
akvays  found,  but  the  examiner  should  proceed  in  a  manner 
that  will  uncover  all  errors  present,  and  if  the  patient  is  very 
young,  say  five  years  old,  then  a  dynamic  measurement  up  to 
within  6  or  7  inches  will  be  wise. 


Question  No.  20.  By  dynamic  skiametry,  when  patients 
are  from  twenty  to  thirty-five  years  of  age,  how  near  should 
measurements  for  refractive  errors  usually  be  made  ? 

Answer  No.  20.    About  15  inches  away  is  near  enough. 

Remarks,  No.  20.  In  noting  these  different  points  for 
varying  ages  the  student  should  exercise  judgment.  If  the 
error  is  hypcropic  then  the  nearer  to  the  limit  of  amplitude  an 
examination  is  made  the  more  of  the  so-called  latent  will  be 
uncovered. 

If  the  error  is  myopic  then  nearness  of  examination  is  not 
always  productive  of  the  best  results,  especially  in  cases  that 
have  never  worn  correcting  lenses. 


Question  No.  21.  By  dynamic  skiametry  where  patients 
are  from  thirty-five  to  fifty  years  of  age,  how  near  should 
measurements  for  refractive  errors  usually  be  made? 


l86  QUESTIONS^    ANSWERS    AND    REMARKS 

Answer  No.  21.    Measure  at  two  points,  13  and  40  inches. 

Remarks,  No.  21.  The  nearer  to  the  so-called  presbyopic 
age  a  patient  approaches  the  more  careful  an  examiner  should 
be  to  not  get  inside  of  the  punctuni  proximiim,  hence  data  from 
two  points  should  be  made. 

Persons  whose  eyes  are  emmetropic  usually  do  not  require 
reading  glasses  until  about  their  forty-seventh  year  of  age. 
But  so  few  eyes  are  really  emmetropic  that  this  age  is  the 
exception  rather  than  the  rule.  Presbyopia,  however,  frequently 
serves  to  uncover  slight  hyperopic  errors  about  the  fortieth 
year  of  age,  and  this  slight  hyperopia  is  sometimes  mistaken  for 
presbyopia,  the  same  as  presbyopia  can  be  mistaken  for  hy- 
peropia if  the  "p  p"  is  lost  sight  of. 


Question  No.  22.  When  patients  are  over  fifty  years  of 
age,  how  should  their  eyes  be  measured? 

Answer  No.  22.    By  both  static  and  dynamic  skiametry. 

Remarks,  No.  22.  It  is  quite  surprising  what  an  active 
accommodation  some  old  persons  retain,  so  whenever  there  is  a 
history  of  eye-strain  an  examiner  should  always  search  deeply 
for  latent  errors. 

The  practice  of  making  three  skiametric  measurements  with 
fixation  at  13,  40  and  240  inches,  is  an  excellent  means  for 
arriving  at  the  correct  judgment  necessary  to  succeed. 


Question  No.  23.  By  dynamic  skiametry,  how  near  should 
measurements  for  presbyopia  be  made  ? 

Answer  No.  23.  Thirteen  to  sixteen  inches,  or  at  the  usual 
reading  point. 

Remarks,  No.  2t,.  Reading  and  working  distances  vary  so 
with  different  persons  that  no  fixed  rule  can  be  laid  down  for 
an  examiner's  guidance.    Questioning  a  patient  as  to  his  occu- 


QUESTIONS,    ANSWERS    AND   REMARKS  187 

pation  and. visual  requirements  often  uncovers  valuable  data. 
Then  following  the  subjective  test  with  a  skiametric  examina- 
tion, where  fixation  and  observation  are  at  the  patient's  indi- 
vidual reading  point,  will  enable  the  skillful  examiner  to  quickly 
detect  over  and  under-connections. 

It  will  be  noted,  in  passing,  that  dynamic  skiametry  thus 
oflfers  the  only  objective  means  known  for  measuring 
presbyopia. 


Question  No.  24.  By  dynamic  skiametry  with  fixation 
at  40  inches  and  observation  at  36  inches,  if  emmetropia  is 
present  what  will  be  the  action  of  the  shadow  ? 

Answer  No.  24.    It  will  move  zvith  the  mirror. 

Remarks,  No.  24.  The  quick  speed  of  the  shadow,  and  the 
vagueness  of  its  definition,  often  show  to  the  skillful  examiner 
that  he  is  close  to  the  point  of  reversal.  The  difference  in 
focal  strength  between  36  and  40  inches  is  only  about  0.12  D., 
and  it  requires  considerable  skill  to  detect  a  difference  of  so 
small  a  quantity. 

It  will  be  remembered,  however,  that  in  pronounced  errors 
the  shadows  are  heavy  and  well  defined,  though  sluggish  in 
motion,  whereas,  in  slight  errors  the  shadows  are  faint,  poorly 
defined  and  rapid  in  motion. 


Question  No.  25.  By  dynamic  skiametry  Avith  fixation 
and  observation  at  38  inches,  if  the  shadow  shows  no  movement, 
either  zvith  or  against  the  plane  mirror,  what  should  an  examiner 
do  in  order  to  determine  the  presence  or  absence  of  hyperme- 
tropiaf 

Answer  No.  25.  Add  plus  spheric  lenses  until  reversal 
occurs.  The  strength  of  the  added  lenses  just  before  this  takes 
place  will  represent  the  error. 


l88  QUESTIONS,    ANSWERS    AND    REMARKS 

Remarks,  No,  25.  This  question  involves  one  of  the 
baffling  points  in  dynamic  skiametry  to  many  who  do  not  go 
into  the  subject  deeply. 

An  eye  with  2.  D.  of  hyperopia  in  fixing  at  a  point  40  inches 
away  makes  3.  D.  of  accommodative  eflfort,  and  by  skiametry 
may  show  no  motion  whatever.  But  if  plits  lenses  are  added 
the  accommodation  will  relax  to  the  point  where  accommodative 
myopia  is  a  factor,  when  the  shadow  will  then  show  an  against 
motion. 


Question  No.  26.  By  dynamic  skiametry  with  fixation  at 
40  inches  and  reversal  in  all  meridians  at  26  inches,  what  is  the 
kind  and  amount  of  the  error? 

Answer  No.  26.    0.50  D.  of  myopia. 

Remarks,  No.  26.  This  question  involves  two  kinds  of 
myopia,  accommodative  and  true,  and  the  difference  between 
where  the  point  of  reversal  ought  to  be  and  where  it  really  is 
represents  the  error. 

This  eye  having  0.50  D.  of  true  myopia  has  a  punctum  re- 
motum  of  80  inches,  and  in  looking  at  an  object  40  inches  away 
it  would  seem  as  though  only  0.50  D.  of  accommodative  effort 
would  be  used.  But  in  fixing  at  40  inches  3  degrees  of  con- 
vergence are  called  for  and  this,  in  turn,  requires  i.  D.  of 
accommodation,  so  it  can  be  readily  seen  why  the  point  of 
reversal  was  less  than  that  of  fixation. 


Question  No.  27.  By  dynamic  skiametry  with  fixation  and 
observation  at  26  inches,  if  an  eye  accepts  a  plus  1.25  D.  S. 
lens  before  reversal  occurs,  what  is  the  error? 

Answer  No.  27.    1.25  D.  of  hypermetropia. 

Remarks,  No.  2y.  The  theories  involved  in  this  question 
cover,  perhaps,  the  simplest  principles  called  for  in  the  dynamic 


QUESTIONS,    ANSWERS    AND   REMARKS  189 

method.  Fixation  and  observation  being  at  a  common  point, 
all  an  examiner  has  to  do  is  to  find  out  how  much  accommo- 
dative relaxation  he  can  obtain. 

An  emmetropic  eye  in  looking  at  an  object  26  inches  away 
makes  an  accommodative  effort  equal  to  1.50  D.  In  this  case, 
however,  the  error  and  the  fixation  called  for  2.75  D.  of 
accommodation,  and  so  when  a  lens  of  plus  1.25  D.  S.  was 
given  the  accommodation  then  relaxed  this  amount.  And  the 
reason  it  did  not  relax  more  than  this  was  because  convergence 
locked  it,  by  interfering  with  a  further  surrender  until  con- 
vergence was  altered. 


Question  No.  28.  Now,  suppose  the  case  in  Question  No. 
2"/  had  shown  a  hyperopia  error  of  0.75  D.  by  the  static 
method,  how  would  this  difference  be  explained  ? 

Answer  No.  28.  As  a  spasm  of  accommodation.  The  dif- 
ference being  what  is  called  a  latent  error. 

Remarks,  No.  28.  Here  is  a  question  in  which  tension  of 
accommodation  is  a  factor.  While  the  eyes  are  fixing  at  a 
distance  it  is  found  that  0.75  D.  is  all  the  relaxation  that  can 
be  obtained,  but  when  this  same  eye  is  exerted  for  a  focal 
adjustment  of  26  inches  then  the  relaxation  is  more,  and  if  the 
■fixation  was  still  nearer  perhaps  the  relaxation  would  be  slightly 
greater. 

It  is  this  known  data  for  different  distances  that  enables  an 
examiner  to  formulate  a  better  prescription  than  if  the  data  was 
limited  to,  say,  subjective  tests  alone. 

In  dynamic  skiametry  it  is  not  contended  that  the  relation- 
ship between  accommodation  and  convergence  is  a  fixed  quan- 
tity. The  "i  to  3"  standard  is  merely  used  to  aid  in  explana- 
tion. Esophoria  and  exophoria  are  factors,  of  course,  the  same 
as  myopia  and  hyperopia.     And  it  is  the  determination  of  the 


IQO  QUESTIONS^    ANSWERS    AND    REMARKS 

special  relationship  in  individual  cases  that  makes  dynamic 
skiametry  of  such  great  value  for,  after  all,  every  case  can  be 
truthfully  called  "special." 


Question  No.  29.  By  dynamic  skiametry  with  fixation 
and  observation  at  40  inches,  suppose  a  plus  i.  D.  S.  lens  can 
be  added  before  reversal  occurs,  but  at  16  inches  a  plus  1.50 
D.  S.  lens  can  be  used  before  reversal  takes  place,  what  condi- 
tion does  this  indicate? 

Answer  No.  29.  Either  so-called  latent  hyperopia,  or  an 
abnormal  relationship  between  accommodation  and  convergence, 

sometimes  termed  "sub-normal  presbyopia." 

Remarks,  No.  29.  The  old  saying  that  "A  rose  by  any 
other  name  smells  just  as  sweet,"  is  applicable  in  the  above 
case,  for  it  really  matters  little,  in  a  practical  sense,  whether 
the  need  of  stronger  glasses  in  reading,  than  are  required  for 
distance,  is  due  to  early  presbyopia,  esophoria  or  latent  hyper- 
opia. What  an  examiner  really  desires  to  find  out  are  the  facts 
in  the  case,  so  he  can  govern  his  judgment  accordingly. 


Question  No.  30.  By  dynamic  skiametry  with  fixation  and 
observation  at  37  inches,  if  it  takes  a  plus  i.  D.  lens  to  cause 
reversal  in  the  vertical  meridian,  and  a  plus  1.50  D.  lens  to 
cause  reversal  in  the  horizontal,  what  is  the  error? 

Answer  No.  30.  i.  D.  of  hyperopia  and  0.50  D.  of  hyper- 
opic  astigmia,  at  axis  90. 

Remarks,  No.  30.  This  is  a  case  of  measuring  the  two 
chief  meridians  of  the  eye.  The  least  refractive  error  repre- 
sents the  spheric  quantity,  while  the  difference  between  the 
two  represents  the  cylindric,  the  axis,  of  course,  being  in  the 
direction  of  least  error. 


QUESTIONS,    ANSWERS    AND   REMARKS  IQI 

Question  No.  31.  By  dynamic  skiametry  with  fixation  at 
40  inches,  the  patient  wearing  a  plus  i.  D.  S.  lens,  if  reversal 
is  found  at  22  inches,  what  is  the  kind  and  amount  of  the  error  ? 

Answer  No.  31.    0.25  D.  of  hyperopia. 

Remarks,  No.  31.  This  question  involves  two  kinds  of 
myopia,  accommodative  and  artificial.  The  accommodative 
represents  i.  D.  and  the  artificial,  i.  D.,  while  the  total  is 
shown  by  the  reversal  point  to  be  only  1.75  D.,  hence  it  fol- 
lows that  hyperopia  must  be  present  to  absorb  the  difference 
between  the  sum  of  the  accommodative  and  the  artificial  myopia, 
which  equals  2.  D.,  and  that  represented  by  the  reversal  point, 
of  1.75  D. 

If  the  reversal  point  had  been  at  18  inches  then  the  error 
would  have  been  0.25  D.  of  true  myopia. 


Question  No.  32.  By  dynamic  skiametry  with  fixation  at 
40  inches  and  reversal  in  the  vertical  meridian  at  22  inches,  and 
in  the  horizontal  at  32  inches,  what  is  the  formula  of  the  lens 
that  will  neutralize  this  error?  The  formula  may  be  written 
two  ways. 

Answer  No.  32. 

• —  0.25  D.  S.  C  —  0-50  D.  C.  180,  or 

.    —  0.75  D.  S.  C  +  0.50  D.  C.  90. 

Remarks,  No,  32.  With  fixation  equal  to  i.  D.  and  re- 
versal at  1.75  D.  the  error  in  the  vertical  meridian  can  be  cor- 
rected with  —  0.75  D.  C.  axis  180.  And  with  fixation  equal  to 
I.  D.  and  reversal  at  1.25  D.  in  the  horizontal  the  error  is 
correctable  with  a  lens  of  —  0.25  D.  C.  axis  90.  These  crossed 
cylinders  transposed  equal  the  formulas  given  in  the  answer. 

Ray-value  corrections,  or  where  the  distance  that  reversal 
occurs  is  noted,  can  always  be  proven  by  lens-value  ones,  or 
where  lenses  are  used  to  produce  reversal,  by  simply  using  the 


192  QUESTIONS,    ANSWERS    AND    REMARKS 

lenses  called  for  by  the  formula  and  then  noting  whether  the 
shadow  behaves  the  same  as  it  would  in  emmetropia. 


Question  No.  33.  By  dynamic  skiametry,  with  fixation 
and  observation  the  same,  where  patient  is  wearing  a  lens 
measuring  -\-  0.25  D.  S.  C  +  0-50  D.  C.  axis  150  and  it  is  found 
that  an  added  lens  power  equal  to  +  0.25  D.  S.  can  be  given 
in  the  60th  meridian  before  reversal  occurs,  but  this  same  lens 
causes  motion  against  in  the  150th  merdian,  what  is  the  correct 
formula  ? 

Answer  No.  33.    +  0.25  D.  S.  C  +  0.75  D,  C.  150. 
•    Remarks,  No.  33.    The  patient's  lens,  as  above,  reduced  to 
its  cylindric  equivalent  gives  a  total  of 

Axis  60  Axis  150 

+  0.25  +  0.75 

If  an  added  +  0.25  D.  can  be  given  in  the  60th  meridian,  but 
not  in  the  150th,  then  0.25  D.  C.  axis  150  is  to  be  added  to  the 
patient's  lens  for  a  new  formula  and  this  transposed  gives 
the  answer. 

Measurements  made  over  a  patient's  own  glasses  offer  a 
very  convenient  means  for  quickly  determining  whether  they 
are  correct  or  not. 

Question  No.  34.  By  dynamic  skiametry  where  patient  is 
wearing  a  lens  of  —  0.50  D.  S.  3  —  0.87  D.  C.  axis  105 
and  it  is  found  that  a  combination  of  +  0.12  D.  S.  3  —  0-25 
D.  C.  axis  15  is  required  to  give  a  slight  motion  with  in  all 
meridians,  fixation  and  observation  being  the  same,  and  made 
at  16  and  40-inch  distances,  what  are  the  correct  formulas  that 
may  be  given? 

Answer  No.  34. 

—  0.63  D.  C.  C  —  1-25  D.  C.  105. 

—  0.63  D.  S.  C  —  0.63  D.  C.  105.    _^  '^^ 

—  1.25  D.  S.  C  +  0.63  D.  C.  15. 


QUESTIONS,    ANSWERS    AND    REMARKS  I93 

Remarks,  No.  34.    The  cylindric  equivalent  of  the  patient's 
lens  together  with  the  added  quantity  shows : 

Axis  ij  A.x-is  10 j 

—  0.50  —  0.50 
-|-  0.12                                             —  0.87 

—  0.25  -|-  0.12 


—  0.63  —  1.25 

Transposition  then  follows. 


Question  No.  35.  By  dynamic  skiametry,  why  should  all 
measurements  be  made  in  a  binocular  manner,  that  is,  by  meas- 
uring first  one  eye  then  the  other,  then  back  to  the  first  one 
again,  and  then  to  the  second,  and  so  on,  with  and  without 
covering  either  eye? 

Answer  No.  35.    To  insure  uniform  muscular  relaxation. 

Remarks,  No.  35.  This  question  involves  co-ordinate  fixa- 
tion, for  as  one  hand  is  usually  more  active  than  the  other  so 
is  one  eye  usually  more  active  than  its  mate,  the  most  active 
one  being  called  the  "fixing  eye,"  the  other  lagging  along  until 
compelled  to  exert  itself. 

It  is  said  that  in  cases  of  convergent  strabismus,  due  to  ]iy- 
peropia,  if  the  fixing  eye  has  its  refractive  error  fully  neutral- 
ized with  lenses  the  straightening  will  occur  even  where  no 
correction  is  given  for  the  deviating  eye.  Thus  showing  the 
supremacy  of  the  eye  of  fixation. 

At  the  beginning  of  a  sJ^iametric  examination  the  operator 
can  not  tell  which  eye  has  the  best  vision,  as  this  is  left  for  the 
subjective  test  to  determine,  and  so  it  sometimes  happens  that 
the  eye  with  the  greatest  error  is  the  one  of  fixation.  It  will 
be  seen,  then,  how  important  it  is  for  the  skiametrist  to  make 
his  examination  in  the  manner  here  referred  to. 


194  QUESTIONS,    ANSWERS    AND   REMARKS 

Question  No.  36.  With  an  csophoria  of  6  degrees,  what 
kind  and  amount  of  refractive  error  should  a  patient  have  in 
order  to  theoretically  harmonize  his  accommodation. 

Answer  No.  36.    About  2.  D.  of  myopia. 

Remarks,  No.  36.  From  the  foregoing  it  will  be  seen  how 
unwise  it  is  to  adapt  prisms  when  the  myopia  present  has  never 
been  corrected. 

A  wise  procedure  in  all  hctcrophoric  cases,  undergoing  their 
first  examination,  is  to  give  correction  for  the  refractive  errors 
found,  and  then  to  await  nature's  efifort  to  adapt  herself  to  the 
new  order  of  relationship  between  accommodation  and  con- 
vergence. 

Prisms  may  have  to  be  given  in  the  end,  but  they  should 
never  be  adapted  at  a  first  sitting  if  it  can  possibly  be  avoided. 


Question  No.  37.  With  2.  D.  of  hyperopia  what  kind  and 
amount  of  hcterophoria  should  be  present  in  order  to  theoret- 
ically harmonize  the  patient's  convergence? 

Answer  No.  37.    About  6  degrees  of  exophoria. 

Remarks,  No.  37.  This  is  the  opposite  of  Question  No.  36. 
If  2.  D.  of  accommodation  calls  for  6  degrees  of  convergence, 
then  an  eye  that  makes  2.  D.  of  accommodation  for  infinity 
must  suppress  this  6  degrees,  or  else  be  exophoric  this  amount, 
hence  it  follows  that  suppressed  convergence  shows  theoretic 
divergence. 

Extrinsic  muscles  that  are  mal-attached,  or  are  aiifected  by 
paralysis,  do  not,  of  course,  come  under  the  same  treatment 
as  those  involving  errors  of  refraction  and  the  consequent  dis- 
turbance in  their  correlation  with  the  intrinsic  muscles. 

It  is  plain,  to  be  sure,  that  an  examiner  at  a  first  sitting  does 
not  know  the  true  cause  of  whatever  heterophoria  he  may  find, 


QUESTIONS,    ANSWERS    AND    REMARKS  I95 

but  if  a  marked  uncorrected  error  of  refraction  is  present  it 
behooves  him  to  neutraHze  as  much  of  this  error  as  he  can 
before  resorting  to  prisms. 


Question  No.  38.  Why  is  convergent  strabismus  some- 
times a  concomitant  of  high  degrees  of  hyperopia f 

Answer  No.  38.  Because  in  the  excessive  muscular  effort 
put  forward  by  the  accommodation,  in  order  to  neutrahze  the 
error,  the  convergence  is  overexerted,  too,  and  then  the  patient 
unconsciously  learns  to  see  better  with  the  fixing  eye  by  sup- 
pressing vision  in  the  deviating  one,  thus  permitting  it  to  turn 
inward  as  far  as  it  likes. 

Remarks,  No.  38.  In  convergent  strabismus  cases,  while 
vision  is  often  suppressed,  the  extrinsic  muscle  action  is  not, 
and  this  therefore  accounts  for  the  marked  deviation  from  the 
standards  controllins:  normal  co-ordination. 


Question  No.  39.  Why  is  divergent  strabismus  sometimes 
a  concomitant  of  high  degrees  of  myopia  f 

Answer  No.  39.  Because,  owing  to  the  non-use  of  accom- 
modation, intrinsic  muscular  effort  is  not  required  to  produce 
focal  adjustment.  Convergence  thus  failing  to  receive  asso- 
ciate stimulation  lags  behind  and,  frequently,  one  eye  learns 
to  suppress  vision,  thereby  losing  its  power  of  co-ordination. 

Remarks,  No.  39.  Short  explanations  of  what  might  be 
called  long  subjects  may  be  pleasing  to  students,  but  they  are 
often  misleading  on  account  of  their  very  shortness.  For  this 
reason  all  searches  after  optomeiric  facts  are  counseled  to  delve 
deeply  into  the  underlying  causes  responsible  for  disturbed  re- 
lationships between  accommodation  and  convergence,  in  all  sorts 
and  conditions  of  cases. 


196  QUESTIONS,    ANSWERS    AND    REMARKS 

The  subjects  of  hcterophoria  and  hctcrotropia  have  been 
touched  upon  here  simply  because  of  their  being  aggravated 
phases  of  many  lesser  disturbances  due  to  the  common  source 
of  inco-ordinate  accommodation  and  convergence. 


■Question  No.  40.  What  is  the  relative  value  of  objective 
optometric  methods  as  compared  to  subjective  ones? 

Answer  No.  40,    As  one  is  to  one. 

Remarks,  No.  40.  Every  optometric  method  of  merit  be- 
comes useful  to  the  optometrist  in  some  case  at  some  time. 
It  therefore  behooves  all  ambitious  examiners  to  thoroughly 
.acquaint  themselves  with  the  principles  underlying  every  opto- 
metric method,  as  this  places  them  in  a  position  to  be  able  to 
judge  for  themselves,  for,  while  the  taking  of  ocular  measure- 
;ments  is  often  comparatively  easy,  it  is  the  formation  of  cor- 
rect judgment  that  in  the  end  can  be  said  to  make  an  examiner's 
ireputation,  while  if  incorrect  it  may  break  it. 


CHAPTER  XII. 

Opinions  of  Others  Regarding  the  Value  of  Skiametry 
IN  General  and  the  Dynamic  Method  in  Particular, 
With  Comments  on  Objective  Versus  Subjective 
Optometry,  and  the  Relationship  of  Accommodation 
AND  Convergence. — Including  Quotations  on  }iIen- 
TAL  Perception,  and  an  Epilogue. 

No  matter  how  meritorious  a  method  may  be  there  are 
always  some  well-meaning  persons  who  prefer  to  hear  the 
opinions  of  others  first,  and  if  these  expressions  are  favorable 
they  feel  warranted  in  taking  up  the  subject  themselves  with  a 
view  to  its  mastery.  Then,  too,  there  are  the  "Doubting 
Thomases"  who  sometimes  get  started  on  the  wrong  line  of 
reasoning  and  become  sadly  tangled,  due,  perhaps,  to  some  early 
misconceptions.  It  may  be  truthfully  stated,  however,  that  all 
reasoners  unquestionably  try  hard  to  do  a  subject  justice,  and 
for  this  reason  their  arguments,  like  the  logic  of  an  opposing 
attorney,  is  well  worth  listening  to,  therefore,  before  closing 
this  little  volume,  it  is  thought  best  to  hear  all  sides  regarding 
dynamic  skiametry  by  quoting  from  sources  independent  of  the 
author,  and  in  this  way  the  pros  and  cons  may  serve  a  useful 
purpose.     The  following  selections  have  therefore  been  made : 

OPINIONS  OF  OTHERS.     A.  W.  Stammer,  in  the  Loudon 
Optician,  for  April,  1910,  writes: 

"I  want  to  describe  one  or  two  simple  experiments  that  any 
optician  with  a  test  case  can  trj%  and  which  will  give  him  a  better 
idea  of  the  way  in  which  the  extrinsic  muscles  work  than  will  weeks 


198  OPINIONS  OF   OTHERS 

of  book  study.  In  all  that  follows  it  must  be  remembered  that  the 
optical  instrument  theorj'  is  completely  ignored,  and  later  it  will  be 
seen  why. 

"The  first  text  book  statement  that  does  nothing  but  confuse  stu- 
dents is  that  there  is  a  definite  co-relation  between  the  functions  of 
accommodation  and  convergence.  This  is  absolutely  true  as  far  as  it  goes, 
and  while  you  regard  the  eye  as  an  instrument  conforming  to  mathe- 
matical laws  requires  no  modification.  It  was  once  believed  that 
there  was  a  co-relation  so  perfect  that  someone  brought  out  a  system 
of  testing  called  dynamic  skiascopy  that  was  based  on  this  fact. 
That  system  failed  for  the  reason  that  there  is  no  fixed  relation 
between  these  two  functions.  Try  the  following  experiments  your- 
self, and  I  think  you  will  see  what  I  mean. 

"Look  at  the  distance  test  charts  through  a  pair  of  minus  two 
spheres  and  you  will  see  each  letter  quite  single.  You  are  accommo- 
dating to  the  amount  of  two  dioptrics,  but  you  are  not  converging, 
or  you  would  see  everything  double.  If  it  were  not  possible  to  use 
these  two  functions  independently,  no  living  person  who  was  hyper- 
metropic could  see  anything  single.  Again ;  look  at  the  chart  through 
a  pair  of  six  degree  prisms  base  out,  and  you  will  still  see  things 
single  a)id  quite  clear.  If  you  were  accommodating  you  would  be 
for  the  time  being  myopic  and  it  would  be  necessary  for  you  to  use  minus 
lenses  to  see  the  chart  clearly.  You  will  see  for  yourself  that  it  is  not 
so;  I  can  myself  read  6/6  with  a  ten  degree  prism  base  out  in  each 
eye.  This  is  found  in  daily  practice  in  the  case  of  a  presbyope  who 
reads  at  thirteen  inches  with  a  -\-  3.0  addition  for  reading.  In  all 
presbyopes  of  a  certain  age  there  is  convergence  for  the  reading  dis- 
tance with  absolutely  no  accommodation. 

"Now,  your  first  experiment  proved  that  you  can  accommodate 
and  not  converge,  and  the  second  that  you  can  converge  and  not 
accommodate.  What  does  control  the  co-relation  of  these  two  func- 
tions? Simply  this,  the  desire  first  for  single  vision,  and  then  for 
clear  vision;  and  these  results  are  obtained  by  co-relation  between  the 
brain  and  the  retina." 

The  Optical  Journal  for  j\lay  26,  1910,  contained  the  fol- 
lowing from  F.  A.  Wambold: 

"It  is  certainly  true  that  testing  by  dynamic  skiascopy  is  a  failure. 
It  always  will  be;  but  the  reason  is  not  found  in  the  fact  that  there 
is    no    fixed    relation    between    convergence    and    accommodation ;    no 


OPINIONS'  OF  OTHERS  I99 

such  fact  exists.  The  opposite  is  true,  as  nature  made  those  two 
functions   work   automatically. 

"It  seems  so  reasonable,  so  natural,  to  think  they  work  in  partner- 
ship. They  are  controlled  by  the  same  wires,  the  third  nerve  through 
which  the  nervous  energy  is  applied.  It  is  the  nervous  supply  way 
back  in  the  brain  that  gives  power  to  those  intrinsic  and  extrinsic 
muscles,  and  to  the  recti  interni  and  externi.  The  same  supply  that 
runs  the  whole  machinery  also  gives  power  to  the  muscles  that  operate 
the  crystalline  lens  and  the  eyeball,  to  cause  the  lens  to  bulge  out, 
and  to  turn  the  eye  out  again  when  turned  in. 

"In  solving  that  question  of  association  of  convergence  and  accom- 
modation, we  must  not  forget  the  function  of  the  recti  externi  muscles 
which  get  their  supply  by  way  of  the  sixth  nerve. 

"Try  the  same  experiments  suggested  by  Mr.  A.  W.  Stammer. 
Put  those  same  minus  2  spheres  in  front  of  your  eyes  and  look  at  the 
test  chart.  If  you  have  the  power  to  overcome  the  glass,  and  in 
addition  any  defect  you  may  happen  to  have,  you  will  of  course  not 
see  double.  Vision  will  be  single.  Why?  Not  because  there  has  been 
no  convergence  in  response  to  the  accommodation  that  was  necessary 
to  bring  the  foci  on  the  retina.  No,  not  that;  they  had  converged; 
they  should  have  and  they  did.  The  wattage  that  went  over  the 
wires  of  the  third  nerve  to  the  ciliary  went  also  over  the  same  wires 
to  the  recti  interni  muscles,  and  pulled  the  eyes  in  at  the  same  ratio 
the  force  was  applied  to  the  ciliary. 

"But  that  created  a  condition  that  should  not  be,  and  in  goes  the 
message  to  the  brain  center  to  turn  on  the  power  on  the  sixth  line 
that  controls  the  externi,  and  the  eyes  are  pulled  straight  again. 
That's  why  j'ou  do  not  see  double,  why  you  have  single  vision  looking 
through  that  minus  2  lens.  If  this  were  not  the  case,  that  is,  if  those 
muscles  had  not  that  function,  that  duty,  then  it  would  have  been 
conclusive  and  logical  to  say,  'no  living  person  who  was  hypermetropic 
could  see  anything  single.' 

"For  the  same  reason  you  see  things  single  looking  through  a  six 
degree  prism.  The  prism,  base  out,  turns  the  eyes  in  and  forces  the 
accommodation,  and  vision  would  be  blurred  if  it  weren't  for  the  fact 
that  nervous  energy  applied  by  way  of  the  sixth  nerve  through  the 
externi  pulled  them  straight  again.  It  will  do  it  every  time,  provided 
the  supply  is  equal  to  the  demand. 

"So  you  see  plainly  that  said  conclusions  are  based  on  false 
grounds  and  test  must  fall. 


200  OPINIONS  OF  OTHERS 

"Look  at  this  statement :  'If  they  converge,  they  will  see  double 
and  the  retina  will  at  once  inform  the  brain  of  the  fact,  and  the  recti 
interni  will  receive  instructions  to  relax  until  the  image  on  each  eye 
is  on  the  fovea.' 

"I  will  concede  the  first,  but  deny  the  return  message,  'the  instruc- 
tion given  by  the  brain  to  relax.'  The  brain  knows  better.  It  knows 
what  those  externi  muscles  are  there  for,  and  turns  on  the  nerve 
wattages  on  the  sixth  nerve  to  stimulate  those  outer  muscles  to  turn 
the  eyes  straight — and  straight  they  come.  That  is  the  function  of  those 
muscles.  We  must  then  not  forget  and  disregard  the  function  of  the 
recti  externi.  Of  course,  that  means  an  extra  supply  to  be  turned 
on  in  that  direction.  If  the  supply  be  insufficient  the  eyes  will  remain 
converging  and  the  person  will  see  double.  Contraction  is  not  the 
cause  that  turns  the  eyes  in,  it  is  an  exhibit  of  the  nervous  energy 
applied.  The  nervous  energy  going  over  the  same  wires  that  control 
the  accommodating  and  converging  muscles  are  the  causative  factors. 
The  nerve-wattage  turned  on  the  sixth  nerve  neutralizes  the  first 
exhibit  and  eyes  come  straight.  See !  It  is  true  that  said  interni 
muscles  relax,  but  not  in  response  to  any  direct  instruction  from  the 
brain  to  do  so.  It  does  it  because  of  the  negative  pull  against  it 
which  exactly  neutralizes  its  contracting  effort;  the  muscles  are  not 
to   blame. 

"The  automatic  relationship  of  convergence  and  accommodation 
stands.  Why  dynamic  skiascopy  is  a  failure;  that  is  another  story. 
The  failure  to  understand  this  phenomenon  has  another  reason.  It 
is  a  lack  of  a  correct  and  complete  understanding  of  the  physical 
laws  of  optics." 

Mr.  H.  B.  AIoore,  in  a  paper  read  before  the  Colorado  State 
Optical  Society,  July,  1910,  stated  as  follows: 

"The  static  method  is  to  place  a  -f  i.oo  D.  lens  in  the  trial  frame 
in  front  of  each  eye;  then  rotate  the  mirror  at  a  distance  of  40  inches 
from  the  eye,  requesting  the  patient  to  look  at  the  test  card  20  feet 
away,  and  if  the  shadow  remains  still  in  the  meridians,  then  the  case 
is  emmetropic,  as  the  -|-  i.oo  D.  lens  just  neutralizes  the  distance 
between  the  optometrist  and  the  patient.  If  the  shadow  moves  with 
the  mirror,  the  case  is  hyperopic,  and  if  it  moves  against,  it  is  myopic, 
and  from  all  retinoscopic  findings  in  this  method,  a  -f-  i.oo  D.  should 
be  deducted. 


OPINIONS   OF  OTHERS  201 

"The  dynamic  method  is  just  the  reverse  of  the  static,  and  a 
system  of  shadow  testing  where  the  accommodation  is  active.  In 
this  method  the  patient  is  directed  to  read  a  small  card  of  different 
size  letters,  placed  on  the  forehead  of  the  optometrist  40  inches  away; 
now  to  do  this  he  has  to  use  i.oo  D.  of  his  accommodation.  Now, 
let  the  deep-thinking  optometrist  follow  this  explanation  closely,  then 
he  can  judge  as  to  the  real  value  of  this  method,  as  it  is  the  writer's 
intention  to  give  facts  and  prove  that  this  method,  zvhich  seems  sO' 
nice  in  theory,  does  not  meet  with  accurate  results  when  in  prac- 
tical use. 

"Here  are  a  few  examples  as  follows — first  case  :  if  the  eye  is  emme- 
tropic the  rays  of  light  will  emerge  parallel  and  the  i.oo  D.  of  accom- 
modation will  converge  these  rays  and  cause  them  to  focus  at  a  dis- 
tance of  40  inches  and  no  motion  will  be  observed  in  either  meridian, 
as  the  I.oo  D.  of  accommodation  used  takes  the  place  of  the  -}-  i-OO  D. 
lens  that  is  used  in  the  static  method. 

"Second  case:  if  the  patient  has  i.oo  D.  of  hyperopia  he  will  be 
obliged  to  use  i.oo  D.  of  his  accommodation  to  see  the  test  card 
clearly  at  a  distance  of  20  feet  and  i.oo  D.  to  read  the  brow  card  at  a 
distance  of  40  inches,  thus  making  a  total  of  2.00  D.  of  accommo- 
dation used. 

"Third  case:  suppose  a  patient  has  i.oo  D.  of  myopia;  his  far 
point  for  distance  vision  is  40  inches  and  the  emergent  rays  will  focus 
at  this  point,  and  the  patient  will  not  use  any  accommodation  to  read 
the  brow  card. 

"Now,  it  is  claimed  by  the  exponents  of  the  dynamic  method  that 
it  is  impossible  to  separate  accommodation  and  convergence  by  placing 
the  plus  lenses  in  front  of  the  eyes,  except  for  hyperopia  they  may 
have.  In  the  first  case  we  find  the  eye  emmetropic  using  i.oo  D.  of 
accommodation.  They  place  plus  lenses  in  front  of  the  eye  and  find 
the  strongest  that  will  be  accepted  without  reversing  the  shadow.  In 
an  emmetropic  eye,  they  state  that  a  -{-  0.25  D.  will  cause  a  reversal 
even  though  the  eye  is  accommodating  i.oo  D. 

"In  the  second  case  we  find  the  eye  using  2.00  D.  of  accommoda- 
tion. They  claim  that  this  eye  will  relax  i.oo  D.,  for  it  is  that  much 
hyperopic,  but  it  cannot  relax  any  of  the  other  i.oo  D.  as  the  con- 
vergence checks  it  so  it  will  not  relax. 

"In  the  third  case,  the  eye  being  myopic  i.oo  D.,  no  accommodation 
is  in  use.    They  place  an  over-correction  of  minus  spheres,  rendering 


202  OPINIONS  OF  OTHERS 

the  refraction  of  this  case  hyperopic.  Then  they  gradually  reduce 
with  minus  spheres  until  they  find  a  point  of  reversal. 

"The  special  advantage  claimed  by  the  exponents  of  this  system 
is :  in  case  of  a  spasm  of  accommodation  sometimes  found  in  a  case 
of  hyperopia.  The  eyes  will  test  myopic  at  40  inches  because  the 
spasm  holds  the  focus  in  front  of  the  retina.  The  spasm  covers  the 
i.oo  D.  of  hyperopia  and  renders  the  eye  myopic  i.oo  D.  and  at  40 
inches  the  motion  is  seen  to  move  against  the  mirror.  Now,  advance 
the  mirror  to  10  inches,  requesting  the  patient  to  read  the  brow  card; 
this  calls  for  4.00  D.  of  accommodation,  and  as  the  patient  has  a 
spasm  of  2.00  D.  covering  his  i.oo  D.  of  hyperopia,  thus  bringing  the 
focus  I.oo  D.  in  front  of  the  retina,  so  it  will  only  be  necessary  for 
him  to  use  3.00  D.  of  his  accommodation.  This  absorbs  the  spasm  and 
gives  a  chance  to  measure  as  much  as  3.00  D.  of  hyperopia ;  but  right 
here  the  dynamic  exponents  claim  that  he  will  accept  just  i.oo  D.,  as 
this  is  the  amount  of  his  hyperopia  and  that  his  convergence  checks 
the  relaxation  at  this  point;  but  does  it? 

"This  whole  system  hinges  upon  their  theory  that  accommodation 
and  convergence  are  so  closely  related  that  by  placing  plus  lenses  in 
front  of  the  eyes  this  relation  cannot  be  disturbed.  If  we  allow  the 
exponents  their  premise  in  an  argument,  we  generally  have  to  admit  it, 
as  their  reasoning  will  be  logical  all  the  way  through.  If  right  here 
we  take  pains  to  experiment  so  we  can  determine  the  truthfulness  of 
their  first  proposition  then  we  w'ill  discover  why  this  method  proves 
up  inaccurate  in  nearly  90  per  cent,  of  all  its  cases.  The  writer 
states  fearlessly  that  convergence  is  not  a  check  upon  accommodation 
and  will  prove  it  by  the  following  experiments : 

"Now,  listen :  if  the  exponents  are  right  in  the  relation  of  these 
two  functions  in  their  shadow  test,  it  surely  ought  to  be  demonstrated 
with  lenses  subjectively.  Take  persons  with  emmetropic  eyes  and  if 
we  place  —  2.50  D.  spheres  in  front  of  their  eyes,  and  in  order  that 
they  can  read  the  20/20  line,  on  the  test  card  20  feet  away,  they  will 
have  to  use  200  D.  of  their  accommodation.  The  20/20  line  on  the 
test  card  20  feet  away  is  perfectly  plain,  bearing  in  mind  that  their 
accommodation  is  fixed  for  16  inches.  This  ought  to  prove  most 
conclusively  to  any  optometrist  that  under  the  above-named  condi- 
tions the  accommodation  can  be  exercised  2.50  D.  while  the  con- 
vergence remains  fixed  for  20  feet.    If  we  were  to  increase  the  strength 


OPINIONS  OF  OTHERS  203 

of  the  minus  spheres,  it  would  produce  diplopia,  thus  showing  that 
2.50  D.  is  the  limit  of  their  power  of  separation  between  these  two 
functions. 

"In  another  experiment  we  find  that  they  can  read  the  20/20  line 
perfectly  with  25  degree  prisms  (half  of  the  amount  over  each  eye) 
base  out.  This  shows  that  they  can  send  a  nerve  force  to  the  internal 
muscles  without  affecting  the  ciliary  muscles  in  the  least.  It  seems  to 
the  writer  as  if  these  two  last  experiments,  which  can  be  made  on 
yourself  or  anyone  else,  ought  to  convince  any  deep-thinking  optom- 
etrist of  the  inaccuracy  of  the  theory  of  the  dynamic  method. 

"In  all  cases  of  hyperopia,  except  the  'squints,'  we  find  these  two 
functions  working  entirely  out  of  harmony  with  each  other,  showing 
the  wonderful  power  of  adjustment  in  nature.  In  all  cases  of  myopia 
we  have  the  same  conditions  reversed,  for  while  the  convergence  is 
fixed  for  20  feet,  the  accommodation  is  nearer  to  the  eye  according 
to  the  myopia." 

In  giving  his  opinion  as  to  what  constituted  the  best  ski- 
amctric  method,  Mr.  Moore  further  stated : 

"The  fogging  method  of  retinoscopy  is  one  that  relaxes  all  accom- 
modation, as  it  is  an  active  accommodation  that  is  responsible  for 
many  errors  in  refraction.  The  test  is  made  by  placing  a  plus  4.00  D. 
lens  before  the  eyes  and  having  the  patient  look  off  into  space.  This 
renders  the  eyes  myopic  and  puts  them  in  a  condition  of  rest.  If 
the  eyes  are  emmetropic,  the  emergent  rays  will  be  parallel  and  a  -f- 
4.00  D.  sphere  will  bring  these  parallel  rays  to  a  focus  at  10  inches  in 
front  of  the  lens.  As  you  observe  the  motion  of  the  shadow  from  40 
inches,  you  will  find  the  eye  decidedly  myopic.  Move  closer  and  closer 
until  you  reach  the  point  of  no  motion.  Measure  from  the  lens  to  the 
mirror,  and  if  the  eyes  are  emmetropic  you  will  find  the  neutral  point 
or  conjugate  foci  to  be  10  inches.  If  your  case  happens  to  be  hyper- 
opic  of  i.oo  D.  the  rays  of  light  will  emerge  i.oo  D.  divergent;  as  it 
requires  i.oo  D.  of  your  -\-  4.00  D.  to  make  these  rays  parallel,  they 
will  be  brought  to  a  focus  13  inc'hes  from  the  eye.  The  motion  will 
reverse  at  this  point.  In  all  cases  of  myopia  the  emergent  rays  are 
convergent  and  the  +  4.00  D.  will  make  them  still  more  convergent. 
If  there  is  i.oo  D.  of  myopia,  the  convergent  rays  would  focus  at  40 
inches  without  any  lens.  Placing  a  4.00  D.  sphere  in  front  of  the  eye 
causes  the  rays  to  focus  at  8  inches  in  front  of  the  lens. 


204  OPINIONS  OF  OTHERS 

"If  we  wish  to  be  exact  in  our  measurements  in  this  or  other 
methods  we  can  attach  a  tape  measure  to  our  trial  frame  and  hold 
the  same  in  one  hand,  while  we  rotate  the  mirror  with  the  other,  at 
the  required  distance.  In  the  fogging  method  this  will  give  you  the 
exact  distance  between  the  lens  and  the  mirror  and  you  will  find  your 
conjugate  foci.  The  rule  to  follows  is:  place  a  +  4.00  D.  sphere  in 
front  of  both  eyes.  Reflect  the  light  with  a  plane  mirror  into  the  eye- 
and  find  the  point  where  there  is  no  motion.  If  it  is  at  the  focal 
point  of  the  lens  10  inches,  the  eye  is  emmetropic." 

Mr.  R.  M.  Lockwood,  of  New  York,  the  scientific  editor 
of  the  Optical  Journal,  in  a  lecture  on  "Dynamic  Optometry,"' 
before  the  Optomctric  Society  of  the  City  of  Neiv  York,  i\Iarcb 
9,  1910,  among  other  things,  said: 

"The  first  variety  of  dynamic  optometry,  to  which  attention  has 
been  called  in  recent  years,  is  the  dynamic  test  with  the  skiascope, 
called  by  the  deviser  of  the  system,  A.  Jay  Cross,  of  New  York, 
'dynamic  skiametry,'  and  elucidated  and  discussed  in  his  work,  'A 
System   of   Ocular   Skiametry.' 

"The  practice  of  dynamic  skiametry  is  based  on  the  theoretically 
strong  inter-relation  of  accommodation  and  convergence,  so  that  if  a 
fixation  chart  be  placed  at  some  point  which  is  near  to  the  eyes  under 
test  the  accommodation  for  that  distance  and  the  convergence  neces- 
sary for  the  same  distance  will  act  together  with  the  result  that,  when 
the  neutralizing  lens  has  been  found  for  that  distance,  the  lenses  in 
the  frame  will  be  the  correction  for  distance,  without  any  allow- 
ance being  made  for  the  point  at  which  the  test  is  made.  As  will  be 
seen,  the  fundamental  difference  between  the  static  method  and 
dynamic  skiametry  is  that  with  the  static  test  the  fixation  chart,  if  any 
is  used,  is  twenty  feet  away,  while  with  the  dynamic  method  the 
fixation  chart  is  brought  to  approximately  the  plane  of  the  observer's 
eye.  In  this  latter  case  it  is  claimed  that  there  is  a  certain  amount 
of  the  accommodation  exerted  which  will  not  relax,  and  this  is  due  to- 
the  fact  that  the  accommodation  and  the  convergence  are  acting  to- 
gether, and  that  the  relation  between  these  two  functions  is  a  very 
strong  one. 

"Suppose  we  find,  with  the  fixation  chart  attached  to  the  skiascope, 
that  it  requires  a  plus  1.50  sphere  to  make  the  shadow  neutral ;  then^ 
according  to  the  theory  of  dynamic  skiametry,  plus  1.50  is  the  cor- 
rection for  distance,  unless  the  accommodation  is  deficient,  no  matter 


OPINIONS  OF  OTHERS  205 

at  what  point  the  test  is  made.  Suppose  the  test  is  made  at  twenty- 
inches  from  the  patient's  eye,  then,  the  fact  that  he  is  accommodating 
for  twenty  inches  and  converging  for  twenty  inches  means  that  the 
ciliary  exerts  two  diopters  of  accommodation  which  it  will  not  relax 
so  long  as  the  fixation  chart  over  the  skiascope  is  fixed,  but  as  this  two 
diopters  will  relax  when  the  attention  passes  from  this  chart  to  the 
distance,  then  the  correction  in  the  frame  is  the  correction  for  dis- 
tance, the  accommodation  supplying  the  amount  of  power  necessary  to 
have  the  attention  come  up  from  distance  to  the  plane  of  the  chart. 
The  author  of  dynamic  skiametry  claims  that  part  of  this  accommo- 
dation, exerted  because  of  the  near  location  of  the  chart  and  the  inter- 
action of  accommodation  and  convergence,  will  be  the  ciliary  spasm 
present,  if  any;  so  that  in  this  supposed  case  the  two  diopters  of  accom- 
modation exerted  because  of  the  location  of  the  fixation  chart  will  be 
made  up  of  the  amount  of  the  spasm  and  in  addition  the  necessary 
extra  effort  required  to  make  up  the  full  amount;  hence  the  method,  he 
claims,  is  an  infallible  detector  of  ciliary  spasm,  and  if  the  full  cor- 
rection as  shown  in  the  trial  frame  cannot  be  worn  at  first  it  may  in 
time,  when  the  spasm  wears  off,  if  it  ever  does.  Incidentally  it  is  found 
according  to  this  theory  that  spasm  of  the  accommodation  is  a  wide- 
spread condition  in  eyes. 

"Now,  I  have  explained  the  fundamental  point  of  dynamic  ski- 
ametry as  the  author  gives  it,  though  I  do  not  accept  it  that  way.  I 
appreciate  the  great  value  of  the  method,  and  it  was  the  consideration 
of  this  method  over  a  space  of  many  months  that  led  me  to  the  for- 
mulating of  another  theory,  which  not  only  takes  in  dynamic  tests 
with  the  skiascope,  but  similar  tests  with  the  trial-case  lenses,  both  of 
which  I  have  grouped  under  the  term  'dynamic  optometry,'  meaning 
the  act  of  testing  eyes  with  the  accommodation  purposely  in  force  for 
the  purpose  of  finding  that  correction  which  will  be  harmonious  for 
any  selected  distance  without  either  the  innervations  involved  being 
too  great  or  too  little;  or,  in  other  words,  the  finding  that  correction 
which  will  give  comfortable  vision." 

T.  G.  Atkinson,  M.D.,  of  Chicago,  editor  of  the  Medical 
Standard,  and  of  the  Optomctric  Department  of  the  National 
Jezveler  and  Optician,  in  the  issue  of  the  latter  pubHcation  for 
August,  1909,  says,  in  part: 

"Speaking  seriously,  we  do  not  believe  that  the  importance  and 
significance  of  dynamic  skiametry  is  anything  like  properly  appreciated. 


206  OPINIONS  OF  OTHERS 

even  by  those  who  are  capable  of  grasping  its  import.  It  is,  in  our 
judgment,  by  far  the  most  momentous  step  in  optometry  since  the  days 
of  Bonders.  Indeed,  as  we  have  previously  remarked,  it  constitutes 
the  line  of  demarcation  between  the  old  and  new  optometry,  just  as 
definitely  as  the  spectroscope  divides  the  old  and  new  astronomy,  and 
in  much  the  same  way,  for  the  essence  of  dynamic  skiametry,  like  that 
of  spectroscopy,  is  that  it  furnishes  a  working  method  of  measuring 
objective  phenomena  in  active  process.  It  is  not  alone  the  useful  and 
valuable  things  which  it  enables  the  optometrist  to  do  that  gives  far- 
reaching  importance  to  the  Cross  system,  but  the  revolutionary  stand- 
point that  it  establishes,  from  which  to  approach  and  handle  problems 
yet  to  arise. 

"Specifically,  the  most  notable  practical  advantages  afforded  by  the 
dynamic  system  of  skiametry  are,  first,  that  it  furnishes  an  exact 
method'of  measuring  refraction  as  it  actually  is,  without  any  allow- 
ances for  the  ciliary  muscle,  and  second,  that  it  utilizes  the  well  known 
principle  of  kinetic  synergism,  by  which  an  active  muscle  will  readily 
accept  needed  relief.  A  further  advantage  of  the  system,  secondary 
from  an  optical  point  of  view,  but  of  prime  importance  from  the 
optometrist's  standpoint,  is  that  it  is  the  only  method  by  which  ob- 
jective refraction  can  be  reliably  carried  out  without  a  cycloplegic,  so 
that  it  is  really  a  crucial,  let  us  say  the  crucial,  pivot  around  which 
revolves  the  entire  sphere  of  optometry  as  an  independent  planet. 

"Eventually,  every  optometrist  will  have  to  understand  and  practice 
dynamic  skiametry.  Eventually,  so  will  every  medical  man  who  hopes 
to  maintain  his  standing  as  a  refractionist.  The  medical  profession  is 
foolishly  engaged  in  the  ostrich  tactics  of  burying  its  head  and  shut- 
ting the  new  order  of  things  out  of  vision,  and  will  some  day  with- 
draw its  silly  head  to  find  that  it  is  outflanked  and  outdistanced.  But 
there  is  nothing  to  exempt  from  the  same  fate  the  equally  foolish 
optometrist  who,  while  he  recognizes  the  importance  of  the  dynamic 
system  and  pays  lip  tribute  to  its  author,  neglects  to  avail  himself  of 
its  principles  and  practice." 

Dr.  H.  J.  Cook,  ex-president  of  the  American  Optical  Asso- 
ciation, in  a  paper  read  before  the  Tennessee  State  Optical 
Society,  July,  1910,  gave  his  opinion  of  dynamic  skiametry  in 
the  following  words : 

"In  cracking  some  nuts  along  this  line  I  will  take  some  of  the 
conundrums  that  have  been  given  from  time  to  time  in  the  optical 


OPINIONS   OF  OTHERS  20/ 

publications  and  try  to  explain  them  by  the  aid  of  a  set  of  rules 
which  I  gave  before  this  body  last  year  at  Nashville,  in  more  detailed 
form.  It  must  be  understood  that  'rules'  do  not  govern  the  shadow 
tests  any  more  than  they  govern  trial-case  refraction,  but  they  will  be 
found  a  great  help  to  the  beginner  in  skiametry,  as  they  fix  the  prin- 
ciples in  the  mind  in  the  same  way  that  the  jingle  of  old  times  fixed 
the  odd  days  of  the  months,  'Thirty  days  hath  September,  April,  June 
and  November.'  This  great  discovery  of  A.  Jay  Cross  is  the  only 
method  by  which  the  total  refraction  of  an  eye  can  be  estimated 
without  the  use  of  drugs.  It  is  the  only  objective  method  that  can  be 
used  in  presbyopia.  It  can  uncover  spasm  when  all  other  systems  fail. 
Its  value  is  so  great  that  it  seems  a  waste  of  time  to  say  that  every 
refractionist  should  use  it — at  least  in  corroboration  of  other  methods. 

"I  take  it  that  you  are  familiar  with  shadow  appearance,  shadow 
motion,  mirrors,  lights,  dark  room  accessories,  and,  above  all,  with  the 
laws  relating  to  conjugate  foci.  We  are  taught  that  rays  from  an 
object  emerge  from  the  eye  along  the  same  path  by  which  they 
entered  it;  thus  the  parallel  rays  emerging  from  the  emmetropic  eye 
and  the  divergent  rays  from  the  hyperopic  eye  must  be  made  con- 
vergent in  order  to  be  intercepted  at  the  crossing  point  by  the 
mirror  of  the  observer.  As  shadow  reversal  is  at  the  focus  conjugate 
with  the  retina,  we  must  set  up  some  form  of  myopia  where  real 
myopia  does  not  exist.  We  have  two  ways  of  doing  this :  by  fixation 
(or  'accommodative  myopia')  or  by  plus  lenses  {artificial  'myopia'). 
We  can  deal  with  all  three  of  the  myopias,  singly  or  combined. 

"Though  the  real  myope  uses  his  accommodation  less  than  the 
emmetrope,  and  the  emmetrope  less  than  the  hyperope — the  addition 
of  artificial  myopia  to  any  of  these  by  lenses,  or  by  accommodation, 
increases  proportionately  the  dioptric  value  of  the  media  traversed  by 
the  rays  from  our  mirror,  and  decreases  proportionately  the  distance 
at  which  shadow  reversal  is  located;  hence  we  are  to  base  our 
diagnosis  of  refractive  errors  upon  differences  between  the  actual 
location  of  reversal  and  the  point  where  normally  it  should  be  found 
in  conjunction  with  the  myopia  we  have  added.  Hence  the  following 
rules : 

"i.  Fixation  distance  (accommodation)  or  plus  lenses,  or  both, 
must  be  used  to  set  up  the  incident  focal  point. 

"2.  Lenses  and  accommodation  are  added  together  in  their  values 
to  create  a  myopic  far  point  (point  of  reversal). 


208  OPINIONS  OF  OTHERS 

"3.  Fixation  and  reversal  points  at  same  distance  indicate  emmc- 
tropia,  or  if  brought  together  with  plus  lenses,  corrected  ametropia. 

"4.     Reversal  found  beyond  fixation  indicates  hyperopia. 

"5.     Reversal  found  inside  fixation  indicates  myopia. 

"6.     In  presbyopia  neutral  point  falls  behind  fixation,  as  hyperopia. 

"The  following  'nuts'  were  given  in  the  Optical  Journal,  page  839, 
by  A.  W.  Stammer  in  an  argument  to  discredit  the  dynamic  system 
on  the  ground  that  accommodation  and  convergence  are  variable  and 
can  be  used  independently.  For  this  reason  he  condemns  the  system 
as  worthless,  and  cites  the  following  cases  to  prove  his  claim : 

"Case  I.  Emmetrope  wearing  minus  2.  D.  reads  20/20ths  zvithout 
convergence,  but  is  using  2.  D.  accommodation  alone. 

"Case  2.  Same  emmetrope  wears  6-degree  prisms  before  each  eye 
base  out;  can  see  normally  at  distance  type  without  accommodation 
while  strongly  converging. 

"Inasmuch  as  dioptric  values  and  not  convergence  govern  in 
shadow  behavior,  his  condemnation  of  the  system  is  based  upon  error. 
In  neither  case  has  one  of  the  'myopias'  been  set  up,  as  required 
by    rule    i. 

"In  case  i,  the  two  diopters  of  accommodative  effort  was  exactly 
balanced  by  the  2.  D.  of  artificial  hyperopia  caused  by  the  minus  lens, 
thus  nothing  was  added  to  the  dioptric  value. 

"Case  2  comes  under  the  same  conditions.  Rule  i  proves  it.  Con- 
vergence added  no  dioptric  value  to  the  eye  in  these  exceptional  cases, 
and  in  case  2,  it  is  to  see  that  the  converging  lines  only  extended 
to  the  outer  surface  of  the  prisms,  becoming  parallel  thereafter. 

"Quizzes  have  gone  the  rounds  of  optical  publications  tending  to 
mystify  those  who  do  not  dig  deeply. 

"Case  3.  One  of  these  asks,  'How  can  you  get  reversal  of  shadow 
at  a  fixation  point,  say  40  inches,  from  an  hyperope  of  i.  D.,  while 
wearing  his  correction  which  makes  him   an  emmetrope?' 

"According  to  rule  i,  accommodative  myopia  of  i.  D.  has  been 
added  to  this  eye  by  fixation,  and  another  i.  D.  by  the  plus  lens, 
—  2.  D.  in  all.  If  the  case  was  an  emmetrope  this  2.  D.  addition 
would  bring  the  reversal  point  up  to  20  inches,  the  same  as  in  real 
myopia  without  artificial  aid.  But  his  hyperopic  divergency  consumes 
I.  D.  of  the  added  power  to  bring  the  divergent  lines  to  parallelism, 
while  the  remaining  i.  D.  can  only  bring  reversal  up  to  the  fixation 
point  of  40  inches.    This  accords  with  rules  i,  2,  3  and  4. 


OPINIONS  OF  OTHERS  2O9 

"Case  4.  Cases  which  seem  to  disprove  rules  should  be  carefully 
examined.  One  in  which  distant  vision  blurs  with  the  weakest  plus 
lens,  but  is  improved  with  a  weak  minus  lens  is  a  hard  nut  for  trial 
case.  Suppose  mirror  shows  reversal  at  32  inches  while  fixation  is  at 
40  inches,  for  example.  By  rule  5  we  suspect  myopia,  because  reversal 
is  found  inside  fixation.  We  move  fixation  card  up  to  this  reversal 
point,  when,  if  true  myopia  exists,  reversal  is  found  at  a  correspond- 
ing distance  forward  (nearer  patient),  which  will  be  in  accordance 
with  the  dioptric  value  added,  or  26  inches.  If,  instead  of  this  forward 
movement,  we  find  that  reversal  has  lagged  behind,  we  may  expect 
spasm.  Moving  fixation  card  still  nearer,  say  to  the  26-inch  reversal 
point,  if  the  case  is  spasm,  of  the  amount  shown  by  the  previous  trial 
lens  used,  reversal  will  now  be  found  behind  the  normally  expected 
position,  and  will  prove  hyperopia,  as  per  rules  i  and  4. 

"In  cases  like  this,  the  spasm  has  been  completely  swallowed  up  in 
the  efifort  forced  by  close  fixation,  which  was  used  in  excess  of  the 
false  myopia  caused  by  the  spasmodic  efifort.  These  cases  are  not  rare, 
and  should  teach  us  to  not  stop  at  reversal,  but  use  several  close 
fixation  points  to  corroborate,  remembering  that  the  principle  is  the 
same  as  in  trial-case  work,  where  we  use  the  strongest  plus  at  infinity, 
With  which  we  get  normal  vision. 

"I  would  not  urge  the  use  of  this  system  in  presbyopia,  owing  to 
the  small  pupils  usually  found,  but  this  is  a  form  of  hyperopia,  and 
premature  presb3'opia  may  often  be  found  in  people  young  enough  to 
be  carelessly  credited  with  the  average  accommodation  given  in 
Donders'  table,  and  it  is  not  rare  therefore,  in  using  the  system,  to 
find  cases  of  young  people  who  need  stronger  glasses  for  reading  than 
for  distance. 

"The  near  point  can  be  located,  as  well  as  the  desired  reading  dis- 
tance in  presbyopia,  by  dynamic  skiametry." 

In  a  paper  on  ''Retinoscopy,"  by  A.  R,  Slader,  read  before 
the  ]\-rmont  State  Optical  Society,  in  July,  1910,  he  says: 

"As  I  have  mentioned  previously,  and  as  all  optometrists  know, 
there  are  two  distinct  methods  of  making  the  test,  called  the  static 
and  dynamic.  The  static  supposes  the  eye  of  the  subject  at  rest — 
the  accommodation  being  inactive — the  focus  being  at  infinity.  By  the 
dynamic  method  the  accommodation  is  in  force,  the  fixation  being 
inside  of  infinity  at  a  certain  definite  point.  By  the  static  method  the 
eye  tested  is   made  artificially  myopic  by  means   of  a  plus  lens  repre- 


2IO  OPINIONS  OF  OTHERS 

senting  the  distance  the  test  is  made  inside  of  infinity;  +0.50  for  80  ins. 
or  2  meters,  +  i-oo  for  40  ins.,  or  one  meter,  +  1.50  for  26  ins..  +  2.00 
for  20  ins.,  etc.  By  the  dynamic  method  the  lens  of  the  eye  takes  the 
place  of  the  artificial  lens,  the  eye  being  held  to  its  position  by  means 
of  a  brow  card  or  lettering  on  a  standard  that  can  be  placed  at  any 
desired  distance  either  back  of  the  observer  or  in  front  of  him.  In 
using  the  static  method  myself  I  usually  work  at  40  ins.  and  place  a 
+  i.oo  D.  lens  before  the  eye  examined  at  once,  then  no  deductions  or 
changes  are  needed  to  be  made  at  the  close  of  the  test,  but  simply  the 
removal  of  the  lens. 

"The  two  methods  differ  only  as  regards  the  treatment  of  the 
accommodation  of  the  subject.  By  the  one  it  is  suppressed;  by  the 
other  it  is  put  into  action.  When  it  is  suppressed  it  is  always  a  ques- 
tion whether  it  is  fully  suppressed  or  whether  it  is  not  exerted  to  a 
more  or  less  degree.  Especially  is  this  true  regarding  this  function  in 
young  people  or  where  there  may  exist  what  is  called  spasm  of  the 
accommodation.  In  subjective  tests  we  have  the  same  problem,  as 
we  all  know,  to  confront.  The  oculist  disposes  of  it  with  the  use 
of  the  cycloplegic,  which  paralyzes  the  function  of  accommodation, 
but  it  is  a  question  whether  this  solution  is  whollj'-  a  happy  one  in 
view  of  the  changes  which  need  to  be  made  in  the  resultant  lenses  to 
make  them  wearable,  and  the  dangerous  nature  of  the  drugs  employed. 

"In  static  retinoscopy  the  darkened  room  helps  to  control  the 
accommodation.  Then  some  use  the  fogging  method,  placing  strong 
lenses  before  the  subject's  eyes  at  first.  It  rests  with  dynamic  ski- 
ascopy, to  my  mind,  however,  to  supply  the  best  means  of  over- 
coming the  difficulty.  This  method  originated  with  A.  Jay  Cross,  and 
is  amply  explained  by  him  in  his  book  entitled  'A  System  of  Ocular 
Skiametry,'  which  should  be  in  the  hands  of  every  optometrist. 

"By  the  dynamic  method  the  accommodation  of  the  subject  is  induced 
to  work,  and  the  theory  is  that  the  greater  the  burden  placed  upon  these 
muscles  the  more  inclined  they  are  to  give  up  any  excess  of  energy 
which  they  might  otherwise  have  exerted — that  it  really  unlocks  spasm 
of  the  accommodation — whether  this  is  strictly  so,  or,  as  some  assert,  it 
only  reveals  that  condition — whether  between  the  co-ordinate  functions 
of  accommodation  and  convergence  there  is  a  fixed  and  immutable 
relationship — a  diopter  of  accommodation  calling  for  a  meter  angle  of 
convergence,  as  the  dynamic  system  theoretically  implies — or,  as  others 
claim,  it  only  shows  whether  the  two  functions  are  in  harmony  at  a 
given  point,  certain   it  is   that  those   who  use  this  method   regularly 


OPINIONS  OF  OTHERS  211 

find  it  of  very  great  value  and  get  very  satisfactory  results.  I,  myself, 
and  I  presume  many  others,  use  both  methods,  though  the  dynamic  is 
the  one  most  relied  upon  in  hyperopic  conditions  with  younger  people. 

"By  the  dynamic  the  test  can  be  made  at  varying  distances  and 
with  fixation  of  the  subject's  eyes  at  different  points.  Thus,  while  the 
retinoscope  is  used  at  40  ins.  or  i  meter,  the  eyes  of  the  subject  can  be 
fixed  at  80  ins.  or  at  any  other  point  inside  of  infinite  distance  and  the 
operation  of  the  shadow  noted.  The  size  of  the  reflex,  rapidity  of  the 
shadow  action,  etc.,  will  vary  according  to  where  and  under  what  con- 
ditions it  is  viewed,  and  with  some  eyes  one  position  is  best  and  with 
some  another.  Again,  in  presb3'opia  it  can  be  used  to  determine  approx- 
imately the  strength  of  lenses  needed  for  the  near  work,  the  examina- 
tion being  made  within  the  reading  distance. 

"But  all  the  work  with  the  retinoscope  needs  to  be  verified  with 
the  subjective  test.  It  does  not  dispense  with  that  form  of  test,  but,  in 
my  opinion,  the  two  should  go  hand  in  hand. 

"In  closing,  I  would  say  that  I  believe  that  every  optometrist  who 
attains  the  highest  success  in  the  profession  must  have  a  working 
knowledge  of  retinoscopy  and  use  it  constantly.  Look  at  its  advan- 
tages, my  brother  optometrists !  First  of  all,  it  is  an  objective  method. 
Such  a  method  appeals  to  the  public  who  furnish  the  eyes  to  be 
tested.  The  subjective  trial-case  method  of  examination,  even  if 
scientific  and  furnishing  accurate  results  to  the  skilful  operator,  looks 
to  the  customer  only  like  a  roundabout  method  of  having  him  select  his 
own  lenses.  To  be  able  to  tell  a  person  what  he  needs  for  glasses, 
without  asking  him  or  her  any  questions,  by  the  simple  flashing  of  a 
light  into  the  person's  eyes,  certainly  gives  the  man  able  to  do  it  a 
professional  standing  in  the  opinion  of  the  client  that  no  subjective 
test  will. 

"Secondly — How  simple  and  inexpensive  the  absolutely  essential 
apparatus  for  the  test  is.  All  that  is  really  needed  is  the  little  ordinary 
hand  retinoscope — a  bright  light  and  a  darkened  room  with  the  trial 
frame  and  lenses,  that  is  all.  Of  course,  adjustable  chairs  and  other 
auxiliaries  are  desirable,  but  good  results  can  be  obtained  under  the 
most  adverse  conditions  by  one  who  is  very  familiar  with  the  test  and 
has  become  an  expert. 

"Thirdly — The  accuracy  of  tlie  results — Of  course  much  of  this 
depends  upon  the  skill  of  the  operator — 'the  man  behind  the  gun,' 
but  so  it  is  with  any  instrument  or  system  of  refraction — but  given  the 


212  OPINIONS  OF  OTHERS 

skilled  operator,  which  practice  will  develop,  and  right  conditions,  and 
I  believe  there  is  no  method  of  measuring  refractive  errors  so  exact. 

"I  have  heard  optometrists  scoflf  at  the  idea  of  measuring  astigma- 
tism with  the  retinoscope  to  the  small  amount  of  a  quarter  of  a 
diopter,  but  such  scoffing  only  proves  that  the  party  is  not  a  user  of 
the  retinoscope,  or  certainly  has  not  acquired  skill  in  diagnosing  errors 
with  it.  To  me  it  is  of  great  value  in  differentiating  J4  diopter,  or 
even  less,  of  astigmatism,  when  unable  to  do  it  for  a  certainty  with 
the  trial  case. 

"Fourthly — It  measures  the  dioptric  system  as  a  whole — not  the 
cornea  only,  like  the  ophthalmometer. 

"I  believe  in  the  subjective  trial-case  test.  I  presume  it  will 
always  remain  an  important  test  and  probably  the  'court  of  last  resort,' 
but  the  little  retinoscope  is  a  mighty  power  in  the  hands  of  the  re- 
fractionist  in  difficult  cases.  With  it  and  a  practical  knowledge  of 
dynamic  skiametry  he  has  an  equipment  that  will  prove  of  immense 
value.  Without  it  he  is  distinctly  at  a  disadvantage  when  he  meets 
adverse  conditions." 

CiiAS.  A.  Jarvis,  in  Kansas  City  Jricchv,  says  : 

"The  real  value  of  dynamic  retinoscopy  lies  in  its  ability  to  un- 
cover latent  hyperopia.  It  is  invariably  successful  in  cases  where  a 
physician  would  use  a  cycloplegic.  For  instance,  if  rotation  of  the 
mirror  shows  no  perceptible  movement  at  first,  and  when  a  plus  lens 
is  placed  before  the  eye  under  examination  and  the  movement  is  not 
against  the  mirror  then  we  may  take  it  that  the  accommodation  has 
relaxed  to  accept  the  plus  lens.  The  power  of  that  lens  which  can  be 
retained  before  the  eye  without  causing  the  shadow  to  move  against 
the  mirror  is  the  amount  of  latent  h\'peropia." 

Under  the  caption  of  "Hozv  Mydriatics  act  in  Skiascopy," 
Mr.  L.  G.  Amsden,  the  well-known  editor  of  the  Canadian 
Optician,  in  the  issue  for  April,  1910,  says: 

"I  am  frequently  in  receipt  of  inquiries  regarding  the  value  of 
retinoscopy  without  the  aid  of  a  mydriatic,  such  queries  being  un- 
doubtedly prompted  by  the  fool  statements  made  in  text-books,  usually 
written  by  medical  men,  in  which  the  stereotyped  phrase  is  always 
found :  'The  test  is,  of  course,  impossible  and  unreliable  without  the 
use  of  the  mydriatic' 


MENTAL    TERCEPTION  213 

"Now,  the  truth  is — and  it  is  becoming  generally  recognized — that 
accurate  results  are  impossible  in  retinoscopy  when  a  mydriatic  is  used, 
owing  to  the  fact  that  the  enlarged  pupil  brings  under  examination 
certain  parts  of  both  cornea  and  lens  that  are  not  used  under  ordinary 
conditions,  and  which  may  possess  curvature  of  an  entirely  dififerent 
nature  to  that  used  in  regular  vision." 

A.  S.  Haskins,  Treasurer  A.  O.  A.,  in  the  Optical  Journal 
of  A'lay  5,  1910,  says : 

"Much  is  being  written  regarding  subjective  and  objective  optom- 
etrj\  Generally,  little  favor  is  given  the  latter.  The  same  ones  who 
speak  against  objective  optometry  are  among  those  who  believe  that 
20  years  will  show  great  advancement  in  optometry.  Certainly,  if 
optometry  advances  it  must  be  along  objective  lines.  Much  of  this 
predicted  advancement  will  be  the  mastery  of  the  present  objective 
methods  by  the  ones  who,  to-day,  think  so  little  of  them." 


MENTAL  PERCEPTION.  As  having  a  bearing  upon 
the  question  of  the  relative  vakie  of  subjective  and  objective 
optometry,  a  short  consideration  of  the  subject  of  mental  per- 
ception, in  general,  may  emphasize  certain  points  showing  why 
it  is  unwise  for  optometrists  to  rely  implicitly  upon  subjective 
data  alone,  extracts  will  therefore  again  be  made  from  the 
pages  of  James'  Briefer  Psychology,  in  which  he  says : 

"Anything  which  affects  our  sense-organs  does  also  more 
than  that :  it  arouses  processes  in  the  hemispheres  which  are 
partly  due  to  the  organization  of  that  organ  by  past  experiences, 
and  the  results  of  which  in  consciousness  are  described  as  ideas 
which  the  sensation  siiggests.  The  first  of  these  ideas  is  that 
of  the  thing  to  which  the  sensible  quality  belongs.  The  con- 
sciousness of  particular  material  things  present  to  sense  is 
nowadays  called  perception.  The  consciousness  of  such  things 
may  be  more  or  less  complete ;  it  may  be  of  the  mere  name  of 
the  thing  and  its  other  essential  attributes,  or  it  may  be  of  the 
thing's  various  remoter  relations.    It  is  impossible  to  draw  any 


214  MENTAL    PERCEPTION 

sharp  line  of  distinction  between  the  barer  and  the  richer  con- 
sciousness, because  the  moment  we  get  beyond  the  first  crude 
sensation  all  our  consciousness  is  of  what  is  suggested,  and  the 
various  suggestions  shade  gradually  into  each  other,  being  one 
and  all  products  of  the  same  psychological  machinery  of  asso- 
ciation. In  the  directer  consciousness  fewer,  in  the  remoter 
more,  associative  processes  are  brought  into  play. 

"Every  concrete  particular  material  thing  is  a  conflux  of 
sensible  qualities,  with  which  we  have  become  acquainted  at 
various  times.  Some  of  these  qualities,  since  they  are  more  con- 
stant, interesting,  or  practically  important,  we  regard  as  essen- 
tial constituents  of  the  thing.  In  a  general  way,  such  are  the 
tangible  shape,  size,  mass,  etc.  Other  properties,  being  more 
fluctuating,  we  regard  as  more  or  less  accidental  or  inessential. 
We  call  the  former  qualities  the  reality,  the  latter  its  appear- 
.ances.  Thus,  I  hear  a  sound,  and  say  a  'horse-car' ;  but  the 
sound  is  not  the  horse-car,  it  is  one  of  the  horse-car's  least 
•important  manifestations.  The  real  horse-car  is  a  feelable,  or 
at  most  a  feelable  and  visible,  thing  which,  in  my  imagination, 
the  sound  calls  up.  So  when  I  get,  as  now,  a  brown  eye- 
picture  with  lines  not  parallel,  and  with  angles  unlike,  and  call 
it  my  big  solid  rectangular  walnut  library-table,  that  picture  is 
not  the  table.  It  is  not  even  like  the  table  as  the  table  is  for 
vision,  when  rightly  seen.  It  is  a  distorted  perspective  view 
of  three  sides  of  what  I  mentally  perceive  (more  or  less)  in  its 
totality  and  undistorted  shape.  The  back  of  the  table,  its  square 
corners,  its  size,  its  heaviness,  are  features  of  which  I  am  con- 
scious when  I  look,  almost  as  I  am  conscious  of  its  name.  The 
suggestion  of  the  name  is  of  course  due  to  mere  custom.  But 
no  less  that  of  the  back,  the  size,  weight,  squareness,  etc. 

"Another  well-known  change  is  when  we  look  at  a  land- 
scape with  our  head  upside  down.  Perception  is  to  a  certain 
extent  baffled  by  this  manoeuvre ;  gradations  of  distance  and 
other  space-determinations  are  made    uncertain ;    the    repro- 


MENTAL    PERCEPTION  215 

ductive  or  associative  processes,  in  short,  decline;  and,  simul- 
taneously with  their  diminution,  the  colors  grow  richer  and 
more  varied,  and  the  contrasts  of  light  and  shade  more  marked. 
The  same  thing  occurs  when  we  turn  a  painting  bottom  up- 
ward. We  lose  much  of  its  meaning,  but,  to  compensate  for 
the  loss,  we  feel  more  freshly  the  value  of  the  mere  tints  and 
shadings,  and  become  aware  of  any  lack  of  purely  sensible 
harmony  or  balance  which  they  may  show.  Just  so,  if  we  lie 
on  the  floor  and  look  up  at  the  mouth  of  a  person  talking 
behind  us,  his  lower  lip  here  takes  the  habitual  place  of  the 
upper  one  upon  our  retina,  and  seems  animated  by  the  most 
extraordinary  and  unnatural  mobility  which  now  strikes  us 
because  (the  associative  processes  being  disturbed  by  the  un- 
accustomed point  of  view)  we  get  it  as  a  naked  sensation  and 
not  as  part  of  a  familiar  object  perceived, 

"There  is  a  whole  batch  of  illusions  which  come  from 
optical  sensation  interpreted  by  us  in  accordance  with  our 
usual  rule,  although  they  are  now  produced  by  an  unusual 
object.  The  stereoscope  is  an  example.  The  eyes  see  a  picture 
apiece,  and  the  two  pictures  are  a  little  disparate,  the  one  seen 
by  the  right  eye  being  a  view  of  the  object  taken  from  a  point 
slightly  to  the  right  of  that  from  which  the  left  eye's  picture  is 
taken.  Pictures  thrown  on  the  two  eyes  by  solid  objects 
present  this  sort  of  disparity,  so  that  we  react  on  the  sensation 
in  our  usual  way,  and  perceive  a  solid.  If  the  pictures  be  ex- 
changed we  perceive  a  hollow  mould  of  the  object,  for  a  hollow 
mould  would  cast  just  such  disparate  pictures  as  these.  Wheat- 
stone's  instrument,  the  pseudoscopc,  allows  us  to  look  at  solid 
objects  and  see  with  each  eye  the  other  eye's  picture.  We  then 
perceive  the  solid  object  hollow,  if  it  he  an  object  'ivhich  might 
probably  be  hollozv,  but  not  otherwise.  Thus  the  perceptive 
process  is  true  to  its  law,  which  is  always  to  react  on  the  sensa- 
tion in  a  determinate  and  figured  fashion  if  possible,  and  in  as 
probable  a  fashion  as  the  case  admits. 


2l6  EPILOGUE 

"Visual  feeling  of  movement  is  produced  by  any  image 
passing  over  the  retina.  Originally,  however,  this  sensation  is 
definitely  referred  neither  to  the  object  nor  to  the  eyes.  Such 
definite  reference  grows  up  later,  and  obeys  certain  simple  laws. 
For  one  thing,  we  believe  objects  to  move  whenever  we  get  the 
retinal  movement-feeling,  but  think  our  eyes  are  still.  This 
gives  rise  to  an  illusion  when,  after  whirling  on  our  heel,  we 
stand  still;  for  then  objects  appear  to  continue  whirling  in  the 
same  direction  in  which,  a  moment  previous,  our  body  actually 
whirled.  The  reason  is  that  our  eyes  are  animated,  under  these 
conditions,  by  an  involuntary  nystagmus,  or  oscillation  in  their 
orbits,  which  may  easily  be  observed  in  anyone  with  vertigo 
after  whirling.  As  these  movements  are  unconscious,  the  retinal 
movement-feelings  which  they  occasion  are  naturally  referred 
to  the  objects  seen.  The  whole  phenomenon  fades  out  after  a 
few  seconds,  and  it  ceases  if  we  voluntarily  fix  our  eyes  upon 
a  given  point. 

"No  sense  gives  sucli  flnctnating  impressions  of  the  same 
object  as  sight  does.  With  no  sense  are  we  so  apt  to  treat  the 
sensations  immediately  given  as  mere  signs ;  with  none  is  the 
invocation  from  memory  of  a  thing,  and  the  consequent  per- 
ception of  the  latter,  so  immediate.  The  'thing'  which  we  per- 
ceive always  resembles  the  object  of  some  absent  sensation, 
usually  another  optical  figure  which  in  our  mind  has  come  to 
be  a  standard  bit  of  reality;  and  it  is  this  incessant  reduction  of 
our  immediately  given  optical  objects  to  more  standard  and 
'real'  forms  which  has  led  some  authors  into  the  mistake  of 
thinking  that  our  optical  sensations  are  originally  and  natively 
of  no  particular  form  at  all." 

EPILOGUE.  Now,  judging  from  the  tenor  of  those 
articles  which  adversely  criticise  Dynamic  Skiamctry,  it  seems 
plain  that  their  authors  do  not  grasp  the  fact  that  the  addition 
of  plus  spheric  lenses  causes  accommodation  to  be  relaxed  in- 


EPILOGUE  217 

stead  of  taxed,  and  that  a  myopic  eye  under  convergence  shows 
more  myopia  than  it  does  under  relaxation,  or  while  trying  to 
see  at  a  distance. 

An  emmetropic  eye,  with  an  abundance  of  amplitude,  in 
looking  at  an  object  13  inches  away  exerts  3.  D.  of 
accommodation.  If  a  minus  i.  D.  S.  lens  is  added,  the 
accommodation  called  for  is  4.  D.,  but  if  a  plus  i.  D.  S.  lens 
is  added,  in  place  of  the  minus  i.  D.,  the  eye  will  not  relax 
to  2.  D.,  and  this  is  because  of  the  correlation  of  convergence. 
If  marked  esophoria  is  present  this  may  not  hold  true,  but 
whatever  relaxation  does  take  place  it  will  be  the  required 
refractive  assistance  necessary  to  harmonize  accommodation 
with  convergence  at  this  distance,  which,  after  all,  is  the  data 
in  the  case  that  the  optometrist  is  looking  for.  Then  if  the 
case  will  not  finally  accept  any  hyperopic  correction  for  infinity 
it  shows  that  a  disturbed  relationship  between  accommodation 
and  convergence  is  present  and  that  heterophoria  or  sub-normal 
ciliary  duction  may  be  factors. 

In  a  myopia  of  i.  D.  convergence  is  not  exerted  while  the 
eye  is  trying  to  look  at  infinity,  but  when  fixation  is  at  40  inches 
convergence  is  then  exerted  3  degrees,  and  this  exertion  un- 
questionably influences  accommodation. 

Once  more  let  it  be  stated  that  dynamic  skiametry  is  not  the 
whole  of  optometry,  but  that  it  gives  an  examiner  valuable  data 
that  can  not  be  obtained  by  any  other  known  method. 

Optometry  covers  the  measurement  of  the  strength  and 
tendencies  of  the  extrinsic  muscles  as  well  as  the  strength  and 
tendencies  of  the  intrinsic  ones,  all  of  which  must  be  taken  into 
consideration.  Testing  amplitude  of  accommodation  and  ampli- 
tude of  convergence  is  very  different  from  determining  the 
refractive  assistance  an  eye  will  readily  accept  for  different 
points  of  fixation. 

"Rules  of  thumb"  are  not  always  to  be  relied  upon  in 
optometry,  for  ocular  conditions  must  be  proven  by  various 


2l8  EPILOGUE 

measurements,  and  then,  after  all  possible  data  is  obtained, 
trained  judgment  is  called  for,  as  an  eye  may  show  a  different 
measurement  for  a  six-meter  distance  than  it  does  for  a  one- 
meter  one,  or  for  a  third  of  a  meter,  and  there  is  a  reason  for 
this  variation  if  an  examiner  is  well  enough  informed  to  as- 
certain it.  Dynamic  skiametry  is  merely  one  method  that  is 
given  to  aid  in  the  solution  of  the  all-important  question: 
What  lenses  should  be  prescribed? 

Why  other  methods  than  subjective  ones  are  needed  in  suc- 
cessful optometry  may  be  readily  inferred  from  the  quotations 
on  mental  perceptions,  here  given,  for  in  practical  optometry  all 
experienced  examiners  know  the  great  variety  of  answers  a 
given  question,  such  as  "which  line  is  the  blackest?"  will  call 
forth  from  different  patients.  Independent  information  that 
will  serve  to  "check  up"  a  patient's  carelessness,  stupidity  or 
misinterpretation  of  a  question  is,  therefore,  no  longer  optional 
in  optometry,  but,  on  the  contrary,  very  vital  to  its  theory  and 
practice  and  to  its  forward  movement  as  a  profession,  to  which, 
it  is  hoped,  dynamic  skiametry  materially  contributes. 


INDEX 


Page 

A  serious    profession 122 

A  simple    experiment    in 

magnifying 151 

A  simple    skiascope 40 

Abduction     112 

Absorption   of   spasm 88 

Abuse  of  lamps 35 

Accommodation     and     con- 
vergence in  emmetropia..  104 
Accommodation     and     con- 
vergence in  hyperopia 106 

Accommodation     and     con- 
vergence in  myopia 107 

Accommodation,  subnormal.  120 

Accommodative   myopia....  86 

Acetylene    lamps 30 

Action  of  shadow 75 

Adduction    112 

Adequate    illumination 22 

Adjustment  of  lamp 23 

"Against  the   mirror" 68 

Alcohol   lamps 34 

Amplimetric 146 

Amplifying    method 139 

Amplitude    of    accommoda- 
tion      132 

Amsden  L.  G 212 

Apparent   light    source 19 

Appearance  of  shadow 69 

Argand   lamps 30 

Arrows     104 

Artificially  created  errors..  50 

"              "       myopia. .  85 

As  a  system 15 

Asbestos  covered  lamps 36 

Asbestos  chimneys 31 

Astigmia,    regular    and    ir- 
regular      117 

Astigmatic  dial   92 

Atkinson,  T.  G 205 

Author's  lamp 36 

"         fixation    stand 92 

"         skiameter    169 

"          skiascope 41 

"         record   blank 145 

Balance    of   accommodation 

and  convergence 104 

Behavior  of  shadow (>"] 


Page 

Binocular    fixation 140 

"           trial    set 156 

"          vision    104 

Black  velvet 60 

Blind  leading  the  blind....  139 

Body  tilting   method 43 

Bowman,   Sir.  William   Pa- 
get   3 

Bracket    skiascope 41 

Breaking  up  of  habits no 

Bright    reflex 94 

Brow   cards 42 

Burnett,  Swan  M 68 

Calcium    carbide 31 

Candle    power 23 

Captain  of  the  visual  ship...  83 

Card-board    model 69 

Card    illumination 61 

Careless    examiners 149 

Carelessness  of  patients....  218 

Case   records    146 

Cases    illustrative 124 

Chimney    covers Z2> 

Ciliary    spasms 108 

Cleaning  the  skiascope 40 

Clonic    spasms 108 

Co-incident    motion 67 

Color   of  shadow 25 

Combining  of  lenses 52 

Cook,   H.  J 206 

Compound   errors . , 70 

Concave    mirrors 39 

Conjugate  foci 68 

Contents     7 

Contraction  of  muscles 108 

Cortical    cataract    131 

Convergence  interfered  with  194 
Corroborative    measure- 

ments    141 

Cost     of     maintenance     of 

lamp    31 

Grain's   disc    159 

Created  myopia  , 85 

Crossing     point  *  of     emer- 
gent   says : 66 

Crowding      on      plus      lens 

quantity     94 

Crystalline    lens  ' 88 


INDEX— Continued 


Page 

Cuignet     5 

Cul-de-sac     138 

C\'cloplegics    140 

Cyliiidric   equivalents    61 

Deaf  persons    I49 

Decomposition      of     carbon 

filament    36 

Demarcation    of    light    and 

shadow     64 

Development   of   skill 116 

DeZeng's     electric      retino- 

scope^    2)7 

DeZeng's  optometer,  phoro- 

meter    and    skiameter....  167 
DeZeng's    standard's    Sche- 
matic  eye    48 

Difference     in     "does"     and 

"ought    to" 67 

Different   measurements....  142 

Difficulties  to  be  overcome.  21 

"          of   skiametry 21 

Disputing  the  count 42 

Donder's    rules 132 

Double   bracket  skiascope...  41 

Duction    tests    122 

Dull    reflexes 76 

Dynamic   skiametry   in   the- 
ory       80 

Dynamic  skiametry  in  prac- 
tice       134 

Economic  stand-point   140 

Elastic  bands   82 

Electric    retinoscope yj 

Emergent   rays    68 

Enlargement    by    magnifica- 
tion      150 

Epilepsy     108 

Epilogue    216 

Equal    innervation    105 

Examination  rooms   27 

Examiner's  nodal   point....  42 

"            own  vision    ....  25 

Experience    115 

Extrinsic   muscles    114 

Facial    light    66 

False    myopia    85 

Fifty  candle  power  lamps..  35 


Page 

Filament  in  lamps    34 

Final  calculations   137 

First  mate  convergence....  83 

Fixation     90 

"         cards     93 

"         stand    92 

"         position     94 

Fixed   rules   unreliable 217 

Formulas    54 

Forty-inch   crossing   point.  .  84 

Fundus    reflex 88 

Gas    lamps    29 

General    health    124 

Geneva   retinoscope    164 

Glass  chimneys    32 

Glory-hole     22 

Guessing 109 

Habit  in  convergence iii 

"         influence    of    loi 

Handle  of  skiascope 40 

Handling  the   skiascope....  43 

Hardy's   wall   bracket 42 

Haskins,    A.     S 213 

Hartridge    81 

Harmonious    convergence..  104 

Head  of  author's  skiameter  171 

Heat  of  lamps    35 

Heterophoric    condition....  100 

History     146 

Holding  the   skiascope 43 

Ideal    conditions 27 

Illiterates     149 

Illumination    28 

Illuminated    fundus 65 

Illuminating  the  fundus....  64 

Illustrations,  list  of 9 

Illustrative  cases  124 

Imbalance    of    accommoda- 
tion      106 

Imitation  of  shadow   69 

Improper    examination 

rooms    27 

Increase   in   electric   current  36 
Increased   convexity   of   the 

crystalline    88 

Infinitj'    194 


INDEX— Continued 


Page 

Influence  of  brightness  ....  22 

"          "    habit     loi 

Innervation 105 

"           in    emmetropia  105 

"           "      hyperopia..  106 

"           "       moypia    ...  107 

Initial   examination    92 

Instruments  as  tools   I53 

Instrument   of  Standart 160 

"            "     Meriden    ...  162 

"            "     Geneva    ....  164 

"            "     DeZeng    . . .  167 

"            "     Author     ....  171 

Intensity   of  illumination...  22 
Involuntary    contraction    of 

muscles     108 

Irregular  astigmia    117 

Iris   diaphragm    33 

Jackson,   Edward    168 

Jarvis,   Chas.  A 212 

Judgment  in   examination..  218 

Keratometric    174 

Klein's    retinoscope    46 

King's   binocular   trial   set.  .  156 

Knowledge    necessary 18 

Kratometric    147 

Lamps    Acetylene 30 

"         Argand     30 

Gas    30 

"        Electric    34 

"        DeZeng's     37 

Welsbach     32 

Latent    errors    loS 

Latent   hyperopia    108 

Law   of  conjugate  foci 68 

Law  of  light  22 

Lens   values    SI 

reduction     55 

"      transposition    56 

Lenticular   myopia    86 

Lockwood,  R.  M 204 

Luminous    retinoscope    37 

Macroscopically     51 

Magnification   of  pupil    ....  150 

Mal-attached  muscles    112 

Measuring    astigmia 115 

"            presbyopia    —  118 


Page 

Mechanical  mydriasis    149 

Median   line    104 

Mental   perception    213 

Meriden    oculometroscope..  162 

Metal   chimneys    31 

Metre  angle   81 

Microscopically     51 

Mirrors    23 

Mixed   astigmatic   condition  50 

Mixed    errors    50 

Mixed  muscle  action  100 

Mobile  lens  action    154 

Model  eyes  of  metal  48 

"          "     "    pasteboard    .  54 

Moore,   H.   B 200 

Multiple  cards   42 

"        fixation     91 

"        methods     138 

Muscle  balance  in  emme- 
tropia      104 

Muscle  balance  in  hypero- 
pia       106 

Muscle  balance  in  myopia..  107 

"         innervation    105 

Muscular  insufficiencies    . . .  105 

Mydriatics     149 

Myopia,  true  and   artificial.  84 

"         accommodative     . .  86 

Nervous   energy    loi 

"       impulses    loi 

Neutralization  at  long  range  51 

Neurometer    104 

Nodal    point 42 

Non-luminous  objects 60 

Non-toxic  skiametry   139 

Normal  relationship  of  ac- 
commodation and  con- 
vergence       104 

Novel   skiascopes    45 

Objective  vs.  subjective  op- 
tometry      213 

Ocular  fundus   65 

"       skiametry  as  a  sys- 
tem      15 

Oculometroscope    162 

Ocular     pupils 151 

Oil   lamps    29 

One  to  three  relationship..  81 


INDEX— Continued 


Page 

Opinions   of  others    197 

Optical     knowledge     neces- 
sary       18 

Optometer   of   DeZeng 167 

Orthophoria     and     Hetero- 

phoria    100 

Other  tests    121 

Parallelism  of  rays 66 

Paralleled      rays     of     light 

converged    20 

■  Parent    157 

Partially  deaf  persons    ....  149 

Peep  holes    23 

Penumbra  double 78 

"           in    skiametry    ...  79 

"     .     single    77 

Perception     213 

Phacometric     146 

Ph9rometer  of   DeZeng.  . . .  167 

Phorometric    147 

Pigmentation    ~;i 

Pink    translucent    paper....  69 

Piano   skiascope    39 

Point  of  reversal 66 

Position   of   light   and   mir- 
ror in  skiametry  94 

Pound  weight    80 

Practice "  of     dynamic     ski- 
ametry     115 

Preface     5 

Prentice,  Charles  F 3 

Presbymetric    147 

Presbyopia  by  skiametry...  119 

Prisms    133 

Principles    of    the    author's 

skiameter     170 

Prismometric     147 

Proper   rooms    27 

Pupils,    large    and    small...  150 

"        why  they  are  red.  .  60 

Quack   doctor    51 

Queen's   schematic   eye 49 

Question  and  answers 173 

Quickness  of  shadow 74 

Ray  bending   power    S3 

Rays    direct    61 

"    rellected   62 


Page 

Ray    values    95 

Recognition  of  ability 59 

Record    blank    145 

Records    144 

Red   pupils    60 

Reduction  of  lenses   51 

Re-education     of-     converg- 
ence and  accommodation  107 

Regular  astigmia    117 

Eeisner's    retinoscope    45 

Relation  of  accommodation 

and  convergence  81 

Relationship      of     extrinsic 

and   intrinsic   muscles....  81 

Relaxed  accommodation  . . .  216 

Reliable    fixation    90 

Research    work 48 

Resourcefulness     148 

Retinal   illumination    63 

target     64 

Retinoscope  of  Geneva 164 

Retinoscopy    S 

Reversal  of  shadow  69 

Rheostats 36 

Risley's  moble  prism   154 

Scar  tissue    117 

Schematic  eyes    48 

"          ej-e    adjustment.  50 

"           eye    practice..  47 

Scissors   movement    118 

Segements     147 

Shadow   actions    67 

"        measuring    69 

Shadow's    imitation 69 

Shadow  phenomena  65 

Size  of   retinal  shadow....  77 

"      "    skiascopic   mirror.  39 

Skiascopes     43 

Skiameter  of  the  author. . . .  171 

Skiametry  as  a  system 15 

Skiametry,  its  value  in  op- 
tometry      16 

Skill    47 

Slader,  A.  R 209 

Sliding  motion    155 

Slow  shadows   75 

Snap  switch    35 

Space  for  examination   ....  27 

Sources  of  illumination  ....  28 


INDEX— Continued 


Page 

Spasmodic  muscle  action  . .  io8 

Spasm  of  accommodation. .  89 

Spiral    filament    34 

Stammer,  A  .W 197 

Standart's    umbrameter. .  . .  160 

Static    method    70 

Straight   line   mirror   move- 
ment      43 

Stumbling  blocks    2t, 

Subjective   optometry    109 

Sub-normal    accommodation  120 

Sub-phenomena   JT) 

Synchronous     76 

Systematic  case  records....  144 

System  of  ocular  skiametry  16 

Theoretic   skiametry    69 

Theories   regarding  dull  re- 
flexes       73 

Theory   of   dynamic   skiam- 
etry      80 

Tension   of   accommodation  in 
"       on  extrinsic  and  in- 
trinsic  muscles    106 

Tonic    spasms    108 

Toxic  skiametry   138 

Transposition   of   lenses....  56 

Trial  case  last   142 

Tropometric     147 

True    myopia    84 


Page 

Umbrameter   of    Standart.  .  160 

Unconscious   habits    loi 

"            muscle    effort..  108 

Unequal   innervation    106 

Unit  lens  action  156 

Units     51 

Use  of  instruments   157 

Value  of  instruments  153 

"       "    skiametry    17 

Various     instruments     used 

in  skiametry   157 

Various  skiascopes 39 

Visible  objects  60 

Visibility   of   fundus    65 

Visual  90 

Visual   fixation    106 

Voltage    35 

Voluntary  muscle  action...  .104 

Wall   bracket    38 

Wambold,    F.    A 198 

Welsbach  lamps    :i2 

Wh}'  the  pupil  appears  red  60 

"With   the    mirror"    67 

Wood  alcohol 34 

Working  lens  ". . .  71 

Wiirdenmann's    lens    rack.  .  158 


Form  L9-Series  4939 


